## JSON-RPC

### `JSONRPCErrorResponse`

interface JSONRPCErrorResponse \{
  jsonrpc: "2.0";
  id?: RequestId;
  error: Error;
}

A response to a request that indicates an error occurred.

jsonrpc: "2.0"

id?: RequestId

error: Error

### `JSONRPCMessage`

JSONRPCMessage: JSONRPCRequest | JSONRPCNotification | JSONRPCResponse

Refers to any valid JSON-RPC object that can be decoded off the wire, or encoded to be sent.

### `JSONRPCNotification`

interface JSONRPCNotification \{
  method: string;
  params?: \{ \[key: string]: any };
  jsonrpc: "2.0";
}

A notification which does not expect a response.

method: string

params?: \{ \[key: string]: any }

jsonrpc: "2.0"

### `JSONRPCRequest`

interface JSONRPCRequest \{
  method: string;
  params?: \{ \[key: string]: any };
  jsonrpc: "2.0";
  id: RequestId;
}

A request that expects a response.

method: string

params?: \{ \[key: string]: any }

jsonrpc: "2.0"

id: RequestId

### `JSONRPCResultResponse`

interface JSONRPCResultResponse \{
  jsonrpc: "2.0";
  id: RequestId;
  result: Result;
}

A successful (non-error) response to a request.

jsonrpc: "2.0"

id: RequestId

result: Result

## Common Types

### `Annotations`

interface Annotations \{
  audience?: Role\[];
  priority?: number;
  lastModified?: string;
}

Optional annotations for the client. The client can use annotations to inform how objects are used or displayed

audience?: Role\[]

Describes who the intended audience of this object or data is.

It can include multiple entries to indicate content useful for multiple audiences (e.g., \["user", "assistant"]).

priority?: number

Describes how important this data is for operating the server.

A value of 1 means "most important," and indicates that the data is effectively required, while 0 means "least important," and indicates that the data is entirely optional.

lastModified?: string

The moment the resource was last modified, as an ISO 8601 formatted string.

Should be an ISO 8601 formatted string (e.g., "2025-01-12T15:00:58Z").

Examples: last activity timestamp in an open file, timestamp when the resource was attached, etc.

### `Cursor`

Cursor: string

An opaque token used to represent a cursor for pagination.

### `EmptyResult`

EmptyResult: Result

A response that indicates success but carries no data.

### `Error`

interface Error \{
  code: number;
  message: string;
  data?: unknown;
}

code: number

The error type that occurred.

message: string

A short description of the error. The message SHOULD be limited to a concise single sentence.

data?: unknown

Additional information about the error. The value of this member is defined by the sender (e.g. detailed error information, nested errors etc.).

### `Icon`

interface Icon \{
  src: string;
  mimeType?: string;
  sizes?: string\[];
  theme?: "light" | "dark";
}

An optionally-sized icon that can be displayed in a user interface.

src: string

A standard URI pointing to an icon resource. May be an HTTP/HTTPS URL or a data: URI with Base64-encoded image data.

Consumers SHOULD takes steps to ensure URLs serving icons are from the same domain as the client/server or a trusted domain.

Consumers SHOULD take appropriate precautions when consuming SVGs as they can contain executable JavaScript.

mimeType?: string

Optional MIME type override if the source MIME type is missing or generic. For example: "image/png", "image/jpeg", or "image/svg+xml".

sizes?: string\[]

Optional array of strings that specify sizes at which the icon can be used. Each string should be in WxH format (e.g., "48x48", "96x96") or "any" for scalable formats like SVG.

If not provided, the client should assume that the icon can be used at any size.

theme?: "light" | "dark"

Optional specifier for the theme this icon is designed for. light indicates the icon is designed to be used with a light background, and dark indicates the icon is designed to be used with a dark background.

If not provided, the client should assume the icon can be used with any theme.

### `LoggingLevel`

The severity of a log message.

These map to syslog message severities, as specified in RFC-5424: [https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1](https://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1)

### `ProgressToken`

ProgressToken: string | number

A progress token, used to associate progress notifications with the original request.

### `RequestId`

RequestId: string | number

A uniquely identifying ID for a request in JSON-RPC.

### `Result`

interface Result \{
\_meta?: \{ \[key: string]: unknown };
\[key: string]: unknown;
}

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `Role`

Role: "user" | "assistant"

The sender or recipient of messages and data in a conversation.

## Content

### `AudioContent`

interface AudioContent \{
  type: "audio";
  data: string;
  mimeType: string;
  annotations?: Annotations;
  \_meta?: \{ \[key: string]: unknown };
}

Audio provided to or from an LLM.

type: "audio"

data: string

The base64-encoded audio data.

mimeType: string

The MIME type of the audio. Different providers may support different audio types.

annotations?: Annotations

Optional annotations for the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `BlobResourceContents`

interface BlobResourceContents \{
  uri: string;
  mimeType?: string;
  \_meta?: \{ \[key: string]: unknown };
  blob: string;
}

uri: string

The URI of this resource.

mimeType?: string

The MIME type of this resource, if known.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

blob: string

A base64-encoded string representing the binary data of the item.

### `ContentBlock`

### `EmbeddedResource`

interface EmbeddedResource \{
  type: "resource";
  resource: TextResourceContents | BlobResourceContents;
  annotations?: Annotations;
  \_meta?: \{ \[key: string]: unknown };
}

The contents of a resource, embedded into a prompt or tool call result.

It is up to the client how best to render embedded resources for the benefit of the LLM and/or the user.

type: "resource"

resource: TextResourceContents | BlobResourceContents

annotations?: Annotations

Optional annotations for the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `ImageContent`

interface ImageContent \{
  type: "image";
  data: string;
  mimeType: string;
  annotations?: Annotations;
  \_meta?: \{ \[key: string]: unknown };
}

An image provided to or from an LLM.

type: "image"

data: string

The base64-encoded image data.

mimeType: string

The MIME type of the image. Different providers may support different image types.

annotations?: Annotations

Optional annotations for the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `ResourceLink`

interface ResourceLink \{
  icons?: Icon\[];
  name: string;
  title?: string;
  uri: string;
  description?: string;
  mimeType?: string;
  annotations?: Annotations;
  size?: number;
  \_meta?: \{ \[key: string]: unknown };
  type: "resource\_link";
}

A resource that the server is capable of reading, included in a prompt or tool call result.

Note: resource links returned by tools are not guaranteed to appear in the results of resources/list requests.

icons?: Icon\[]

Optional set of sized icons that the client can display in a user interface.

Clients that support rendering icons MUST support at least the following MIME types:

image/png - PNG images (safe, universal compatibility)
image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)

Clients that support rendering icons SHOULD also support:

image/svg+xml - SVG images (scalable but requires security precautions)
image/webp - WebP images (modern, efficient format)

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

uri: string

The URI of this resource.

description?: string

A description of what this resource represents.

This can be used by clients to improve the LLM's understanding of available resources. It can be thought of like a "hint" to the model.

mimeType?: string

The MIME type of this resource, if known.

annotations?: Annotations

Optional annotations for the client.

size?: number

The size of the raw resource content, in bytes (i.e., before base64 encoding or any tokenization), if known.

This can be used by Hosts to display file sizes and estimate context window usage.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

type: "resource\_link"

### `TextContent`

interface TextContent \{
  type: "text";
  text: string;
  annotations?: Annotations;
  \_meta?: \{ \[key: string]: unknown };
}

Text provided to or from an LLM.

type: "text"

text: string

The text content of the message.

annotations?: Annotations

Optional annotations for the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `TextResourceContents`

interface TextResourceContents \{
  uri: string;
  mimeType?: string;
  \_meta?: \{ \[key: string]: unknown };
  text: string;
}

uri: string

The URI of this resource.

mimeType?: string

The MIME type of this resource, if known.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

text: string

The text of the item. This must only be set if the item can actually be represented as text (not binary data).

## `completion/complete`

### `CompleteRequest`

interface CompleteRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "completion/complete";
  params: CompleteRequestParams;
}

A request from the client to the server, to ask for completion options.

jsonrpc: "2.0"

id: RequestId

method: "completion/complete"

params: CompleteRequestParams

### `CompleteRequestParams`

interface CompleteRequestParams \{
  \_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
  ref: PromptReference | ResourceTemplateReference;
  argument: \{ name: string; value: string };
  context?: \{ arguments?: \{ \[key: string]: string } };
}

Parameters for a completion/complete request.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

ref: PromptReference | ResourceTemplateReference

argument: \{ name: string; value: string }

The argument's information

Type Declaration

name: string
The name of the argument
value: string
The value of the argument to use for completion matching.

context?: \{ arguments?: \{ \[key: string]: string } }

Additional, optional context for completions

Type Declaration

Optionalarguments?: \{ \[key: string]: string }
Previously-resolved variables in a URI template or prompt.

### `CompleteResult`

interface CompleteResult \{
  \_meta?: \{ \[key: string]: unknown };
  completion: \{ values: string\[]; total?: number; hasMore?: boolean };
  \[key: string]: unknown;
}

The server's response to a completion/complete request

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

completion: \{ values: string\[]; total?: number; hasMore?: boolean }

Type Declaration

values: string\[]
An array of completion values. Must not exceed 100 items.
Optionaltotal?: number
The total number of completion options available. This can exceed the number of values actually sent in the response.
OptionalhasMore?: boolean
Indicates whether there are additional completion options beyond those provided in the current response, even if the exact total is unknown.

### `PromptReference`

interface PromptReference \{
  name: string;
  title?: string;
  type: "ref/prompt";
}

Identifies a prompt.

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

type: "ref/prompt"

### `ResourceTemplateReference`

interface ResourceTemplateReference \{
type: "ref/resource";
uri: string;
}

A reference to a resource or resource template definition.

type: "ref/resource"

uri: string

The URI or URI template of the resource.

## `elicitation/create`

### `ElicitRequest`

interface ElicitRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "elicitation/create";
  params: ElicitRequestParams;
}

A request from the server to elicit additional information from the user via the client.

jsonrpc: "2.0"

id: RequestId

method: "elicitation/create"

params: ElicitRequestParams

### `ElicitRequestParams`

ElicitRequestParams: ElicitRequestFormParams | ElicitRequestURLParams

The parameters for a request to elicit additional information from the user via the client.

### `ElicitResult`

interface ElicitResult \{
  \_meta?: \{ \[key: string]: unknown };
  action: "accept" | "decline" | "cancel";
  content?: \{ \[key: string]: string | number | boolean | string\[] };
  \[key: string]: unknown;
}

The client's response to an elicitation request.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

action: "accept" | "decline" | "cancel"

The user action in response to the elicitation.

"accept": User submitted the form/confirmed the action
"decline": User explicitly decline the action
"cancel": User dismissed without making an explicit choice

content?: \{ \[key: string]: string | number | boolean | string\[] }

The submitted form data, only present when action is "accept" and mode was "form". Contains values matching the requested schema. Omitted for out-of-band mode responses.

### `BooleanSchema`

interface BooleanSchema \{
  type: "boolean";
  title?: string;
  description?: string;
  default?: boolean;
}

type: "boolean"

title?: string

description?: string

default?: boolean

### `ElicitRequestFormParams`

interface ElicitRequestFormParams \{
  task?: TaskMetadata;
  \_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
  mode?: "form";
  message: string;
  requestedSchema: \{
    \$schema?: string;
    type: "object";
    properties: \{ \[key: string]: PrimitiveSchemaDefinition };
    required?: string\[];
  };
}

The parameters for a request to elicit non-sensitive information from the user via a form in the client.

task?: TaskMetadata

If specified, the caller is requesting task-augmented execution for this request. The request will return a CreateTaskResult immediately, and the actual result can be retrieved later via tasks/result.

Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

mode?: "form"

The elicitation mode.

message: string

The message to present to the user describing what information is being requested.

requestedSchema: \{ \$schema?: string; type: "object"; properties: \{ \[key: string]: PrimitiveSchemaDefinition }; required?: string\[]; }

A restricted subset of JSON Schema. Only top-level properties are allowed, without nesting.

### `ElicitRequestURLParams`

interface ElicitRequestURLParams \{
  task?: TaskMetadata;
  \_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
  mode: "url";
  message: string;
  elicitationId: string;
  url: string;
}

The parameters for a request to elicit information from the user via a URL in the client.

task?: TaskMetadata

Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

mode: "url"

The elicitation mode.

message: string

The message to present to the user explaining why the interaction is needed.

elicitationId: string

The ID of the elicitation, which must be unique within the context of the server. The client MUST treat this ID as an opaque value.

url: string

The URL that the user should navigate to.

### `EnumSchema`

EnumSchema:
  | SingleSelectEnumSchema
  | MultiSelectEnumSchema
  | LegacyTitledEnumSchema

### `LegacyTitledEnumSchema`

interface LegacyTitledEnumSchema \{
  type: "string";
  title?: string;
  description?: string;
  enum: string\[];
  enumNames?: string\[];
  default?: string;
}

Use TitledSingleSelectEnumSchema instead. This interface will be removed in a future version.

type: "string"

title?: string

description?: string

enum: string\[]

enumNames?: string\[]

(Legacy) Display names for enum values. Non-standard according to JSON schema 2020-12.

default?: string

### `MultiSelectEnumSchema`

MultiSelectEnumSchema:
| UntitledMultiSelectEnumSchema
| TitledMultiSelectEnumSchema

### `NumberSchema`

interface NumberSchema \{
  type: "number" | "integer";
  title?: string;
  description?: string;
  minimum?: number;
  maximum?: number;
  default?: number;
}

type: "number" | "integer"

title?: string

description?: string

minimum?: number

maximum?: number

default?: number

### `PrimitiveSchemaDefinition`

PrimitiveSchemaDefinition:
  | StringSchema
  | NumberSchema
  | BooleanSchema
  | EnumSchema

Restricted schema definitions that only allow primitive types without nested objects or arrays.

### `SingleSelectEnumSchema`

SingleSelectEnumSchema:
| UntitledSingleSelectEnumSchema
| TitledSingleSelectEnumSchema

### `StringSchema`

interface StringSchema \{
  type: "string";
  title?: string;
  description?: string;
  minLength?: number;
  maxLength?: number;
  format?: "uri" | "email" | "date" | "date-time";
  default?: string;
}

type: "string"

title?: string

description?: string

minLength?: number

maxLength?: number

format?: "uri" | "email" | "date" | "date-time"

default?: string

### `TitledMultiSelectEnumSchema`

interface TitledMultiSelectEnumSchema \{
  type: "array";
  title?: string;
  description?: string;
  minItems?: number;
  maxItems?: number;
  items: \{ anyOf: \{ const: string; title: string }\[] };
  default?: string\[];
}

Schema for multiple-selection enumeration with display titles for each option.

type: "array"

title?: string

Optional title for the enum field.

description?: string

Optional description for the enum field.

minItems?: number

Minimum number of items to select.

maxItems?: number

Maximum number of items to select.

items: \{ anyOf: \{ const: string; title: string }\[] }

Schema for array items with enum options and display labels.

Type Declaration

anyOf: \{ const: string; title: string }\[]
Array of enum options with values and display labels.

default?: string\[]

Optional default value.

### `TitledSingleSelectEnumSchema`

interface TitledSingleSelectEnumSchema \{
  type: "string";
  title?: string;
  description?: string;
  oneOf: \{ const: string; title: string }\[];
  default?: string;
}

Schema for single-selection enumeration with display titles for each option.

type: "string"

title?: string

Optional title for the enum field.

description?: string

Optional description for the enum field.

oneOf: \{ const: string; title: string }\[]

Array of enum options with values and display labels.

Type Declaration

const: string
The enum value.
title: string
Display label for this option.

default?: string

Optional default value.

### `UntitledMultiSelectEnumSchema`

interface UntitledMultiSelectEnumSchema \{
  type: "array";
  title?: string;
  description?: string;
  minItems?: number;
  maxItems?: number;
  items: \{ type: "string"; enum: string\[] };
  default?: string\[];
}

Schema for multiple-selection enumeration without display titles for options.

type: "array"

title?: string

Optional title for the enum field.

description?: string

Optional description for the enum field.

minItems?: number

Minimum number of items to select.

maxItems?: number

Maximum number of items to select.

items: \{ type: "string"; enum: string\[] }

Schema for the array items.

Type Declaration

type: "string"
enum: string\[]
Array of enum values to choose from.

default?: string\[]

Optional default value.

### `UntitledSingleSelectEnumSchema`

interface UntitledSingleSelectEnumSchema \{
  type: "string";
  title?: string;
  description?: string;
  enum: string\[];
  default?: string;
}

Schema for single-selection enumeration without display titles for options.

type: "string"

title?: string

Optional title for the enum field.

description?: string

Optional description for the enum field.

enum: string\[]

Array of enum values to choose from.

default?: string

Optional default value.

## `initialize`

### `InitializeRequest`

interface InitializeRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "initialize";
  params: InitializeRequestParams;
}

This request is sent from the client to the server when it first connects, asking it to begin initialization.

jsonrpc: "2.0"

id: RequestId

method: "initialize"

params: InitializeRequestParams

### `InitializeRequestParams`

interface InitializeRequestParams \{
  \_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
  protocolVersion: string;
  capabilities: ClientCapabilities;
  clientInfo: Implementation;
}

Parameters for an initialize request.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

protocolVersion: string

The latest version of the Model Context Protocol that the client supports. The client MAY decide to support older versions as well.

capabilities: ClientCapabilities

clientInfo: Implementation

### `InitializeResult`

interface InitializeResult \{
  \_meta?: \{ \[key: string]: unknown };
  protocolVersion: string;
  capabilities: ServerCapabilities;
  serverInfo: Implementation;
  instructions?: string;
  \[key: string]: unknown;
}

After receiving an initialize request from the client, the server sends this response.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

protocolVersion: string

The version of the Model Context Protocol that the server wants to use. This may not match the version that the client requested. If the client cannot support this version, it MUST disconnect.

capabilities: ServerCapabilities

serverInfo: Implementation

instructions?: string

Instructions describing how to use the server and its features.

This can be used by clients to improve the LLM's understanding of available tools, resources, etc. It can be thought of like a "hint" to the model. For example, this information MAY be added to the system prompt.

### `ClientCapabilities`

interface ClientCapabilities \{
  experimental?: \{ \[key: string]: object };
  roots?: \{ listChanged?: boolean };
  sampling?: \{ context?: object; tools?: object };
  elicitation?: \{ form?: object; url?: object };
  tasks?: \{
    list?: object;
    cancel?: object;
    requests?: \{
      sampling?: \{ createMessage?: object };
      elicitation?: \{ create?: object };
    };
  };
}

Capabilities a client may support. Known capabilities are defined here, in this schema, but this is not a closed set: any client can define its own, additional capabilities.

experimental?: \{ \[key: string]: object }

Experimental, non-standard capabilities that the client supports.

roots?: \{ listChanged?: boolean }

Present if the client supports listing roots.

Type Declaration

OptionallistChanged?: boolean
Whether the client supports notifications for changes to the roots list.

sampling?: \{ context?: object; tools?: object }

Present if the client supports sampling from an LLM.

Type Declaration

Optionalcontext?: object
Whether the client supports context inclusion via includeContext parameter. If not declared, servers SHOULD only use includeContext: "none" (or omit it).
Optionaltools?: object
Whether the client supports tool use via tools and toolChoice parameters.

elicitation?: \{ form?: object; url?: object }

Present if the client supports elicitation from the server.

tasks?: \{ list?: object; cancel?: object; requests?: \{ sampling?: \{ createMessage?: object }; elicitation?: \{ create?: object }; }; }

Present if the client supports task-augmented requests.

Type Declaration

Optionallist?: object
Whether this client supports tasks/list.
Optionalcancel?: object
Whether this client supports tasks/cancel.
Optionalrequests?: \{ sampling?: \{ createMessage?: object }; elicitation?: \{ create?: object } }
Specifies which request types can be augmented with tasks.
- Optionalsampling?: \{ createMessage?: object }
  Task support for sampling-related requests.
  - OptionalcreateMessage?: object
    Whether the client supports task-augmented sampling/createMessage requests.
- Optionalelicitation?: \{ create?: object }
  Task support for elicitation-related requests.
  - Optionalcreate?: object
    Whether the client supports task-augmented elicitation/create requests.

### `Implementation`

interface Implementation \{
  icons?: Icon\[];
  name: string;
  title?: string;
  version: string;
  description?: string;
  websiteUrl?: string;
}

Describes the MCP implementation.

icons?: Icon\[]

Optional set of sized icons that the client can display in a user interface.

Clients that support rendering icons MUST support at least the following MIME types:

image/png - PNG images (safe, universal compatibility)
image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)

Clients that support rendering icons SHOULD also support:

image/svg+xml - SVG images (scalable but requires security precautions)
image/webp - WebP images (modern, efficient format)

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

version: string

description?: string

An optional human-readable description of what this implementation does.

This can be used by clients or servers to provide context about their purpose and capabilities. For example, a server might describe the types of resources or tools it provides, while a client might describe its intended use case.

websiteUrl?: string

An optional URL of the website for this implementation.

### `ServerCapabilities`

interface ServerCapabilities \{
  experimental?: \{ \[key: string]: object };
  logging?: object;
  completions?: object;
  prompts?: \{ listChanged?: boolean };
  resources?: \{ subscribe?: boolean; listChanged?: boolean };
  tools?: \{ listChanged?: boolean };
  tasks?: \{
    list?: object;
    cancel?: object;
    requests?: \{ tools?: \{ call?: object } };
  };
}

Capabilities that a server may support. Known capabilities are defined here, in this schema, but this is not a closed set: any server can define its own, additional capabilities.

experimental?: \{ \[key: string]: object }

Experimental, non-standard capabilities that the server supports.

logging?: object

Present if the server supports sending log messages to the client.

completions?: object

Present if the server supports argument autocompletion suggestions.

prompts?: \{ listChanged?: boolean }

Present if the server offers any prompt templates.

Type Declaration

OptionallistChanged?: boolean
Whether this server supports notifications for changes to the prompt list.

resources?: \{ subscribe?: boolean; listChanged?: boolean }

Present if the server offers any resources to read.

Type Declaration

Optionalsubscribe?: boolean
Whether this server supports subscribing to resource updates.
OptionallistChanged?: boolean
Whether this server supports notifications for changes to the resource list.

tools?: \{ listChanged?: boolean }

Present if the server offers any tools to call.

Type Declaration

OptionallistChanged?: boolean
Whether this server supports notifications for changes to the tool list.

tasks?: \{ list?: object; cancel?: object; requests?: \{ tools?: \{ call?: object } }; }

Present if the server supports task-augmented requests.

Type Declaration

Optionallist?: object
Whether this server supports tasks/list.
Optionalcancel?: object
Whether this server supports tasks/cancel.
Optionalrequests?: \{ tools?: \{ call?: object } }
Specifies which request types can be augmented with tasks.
- Optionaltools?: \{ call?: object }
  Task support for tool-related requests.
  - Optionalcall?: object
    Whether the server supports task-augmented tools/call requests.

## `logging/setLevel`

### `SetLevelRequest`

interface SetLevelRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "logging/setLevel";
  params: SetLevelRequestParams;
}

A request from the client to the server, to enable or adjust logging.

jsonrpc: "2.0"

id: RequestId

method: "logging/setLevel"

params: SetLevelRequestParams

### `SetLevelRequestParams`

interface SetLevelRequestParams \{
\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
level: LoggingLevel;
}

Parameters for a logging/setLevel request.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

level: LoggingLevel

The level of logging that the client wants to receive from the server. The server should send all logs at this level and higher (i.e., more severe) to the client as notifications/message.

## `notifications/cancelled`

### `CancelledNotification`

interface CancelledNotification \{
  jsonrpc: "2.0";
  method: "notifications/cancelled";
  params: CancelledNotificationParams;
}

This notification can be sent by either side to indicate that it is cancelling a previously-issued request.

The request SHOULD still be in-flight, but due to communication latency, it is always possible that this notification MAY arrive after the request has already finished.

This notification indicates that the result will be unused, so any associated processing SHOULD cease.

A client MUST NOT attempt to cancel its initialize request.

For task cancellation, use the tasks/cancel request instead of this notification.

jsonrpc: "2.0"

method: "notifications/cancelled"

params: CancelledNotificationParams

### `CancelledNotificationParams`

interface CancelledNotificationParams \{
  \_meta?: \{ \[key: string]: unknown };
  requestId?: RequestId;
  reason?: string;
}

Parameters for a notifications/cancelled notification.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

requestId?: RequestId

The ID of the request to cancel.

This MUST correspond to the ID of a request previously issued in the same direction. This MUST be provided for cancelling non-task requests. This MUST NOT be used for cancelling tasks (use the tasks/cancel request instead).

reason?: string

An optional string describing the reason for the cancellation. This MAY be logged or presented to the user.

## `notifications/initialized`

### `InitializedNotification`

interface InitializedNotification \{
  jsonrpc: "2.0";
  method: "notifications/initialized";
  params?: NotificationParams;
}

This notification is sent from the client to the server after initialization has finished.

jsonrpc: "2.0"

method: "notifications/initialized"

params?: NotificationParams

## `notifications/tasks/status`

### `TaskStatusNotification`

interface TaskStatusNotification \{
  jsonrpc: "2.0";
  method: "notifications/tasks/status";
  params: TaskStatusNotificationParams;
}

An optional notification from the receiver to the requestor, informing them that a task's status has changed. Receivers are not required to send these notifications.

jsonrpc: "2.0"

method: "notifications/tasks/status"

params: TaskStatusNotificationParams

### `TaskStatusNotificationParams`

TaskStatusNotificationParams: NotificationParams & Task

Parameters for a notifications/tasks/status notification.

## `notifications/message`

### `LoggingMessageNotification`

interface LoggingMessageNotification \{
  jsonrpc: "2.0";
  method: "notifications/message";
  params: LoggingMessageNotificationParams;
}

JSONRPCNotification of a log message passed from server to client. If no logging/setLevel request has been sent from the client, the server MAY decide which messages to send automatically.

jsonrpc: "2.0"

method: "notifications/message"

params: LoggingMessageNotificationParams

### `LoggingMessageNotificationParams`

interface LoggingMessageNotificationParams \{
  \_meta?: \{ \[key: string]: unknown };
  level: LoggingLevel;
  logger?: string;
  data: unknown;
}

Parameters for a notifications/message notification.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

level: LoggingLevel

The severity of this log message.

logger?: string

An optional name of the logger issuing this message.

data: unknown

The data to be logged, such as a string message or an object. Any JSON serializable type is allowed here.

## `notifications/progress`

### `ProgressNotification`

interface ProgressNotification \{
  jsonrpc: "2.0";
  method: "notifications/progress";
  params: ProgressNotificationParams;
}

An out-of-band notification used to inform the receiver of a progress update for a long-running request.

jsonrpc: "2.0"

method: "notifications/progress"

params: ProgressNotificationParams

### `ProgressNotificationParams`

interface ProgressNotificationParams \{
  \_meta?: \{ \[key: string]: unknown };
  progressToken: ProgressToken;
  progress: number;
  total?: number;
  message?: string;
}

Parameters for a notifications/progress notification.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

progressToken: ProgressToken

The progress token which was given in the initial request, used to associate this notification with the request that is proceeding.

progress: number

The progress thus far. This should increase every time progress is made, even if the total is unknown.

total?: number

Total number of items to process (or total progress required), if known.

message?: string

An optional message describing the current progress.

## `notifications/prompts/list_changed`

### `PromptListChangedNotification`

interface PromptListChangedNotification \{
  jsonrpc: "2.0";
  method: "notifications/prompts/list\_changed";
  params?: NotificationParams;
}

An optional notification from the server to the client, informing it that the list of prompts it offers has changed. This may be issued by servers without any previous subscription from the client.

jsonrpc: "2.0"

method: "notifications/prompts/list\_changed"

params?: NotificationParams

## `notifications/resources/list_changed`

### `ResourceListChangedNotification`

interface ResourceListChangedNotification \{
  jsonrpc: "2.0";
  method: "notifications/resources/list\_changed";
  params?: NotificationParams;
}

An optional notification from the server to the client, informing it that the list of resources it can read from has changed. This may be issued by servers without any previous subscription from the client.

jsonrpc: "2.0"

method: "notifications/resources/list\_changed"

params?: NotificationParams

## `notifications/resources/updated`

### `ResourceUpdatedNotification`

interface ResourceUpdatedNotification \{
  jsonrpc: "2.0";
  method: "notifications/resources/updated";
  params: ResourceUpdatedNotificationParams;
}

A notification from the server to the client, informing it that a resource has changed and may need to be read again. This should only be sent if the client previously sent a resources/subscribe request.

jsonrpc: "2.0"

method: "notifications/resources/updated"

params: ResourceUpdatedNotificationParams

### `ResourceUpdatedNotificationParams`

interface ResourceUpdatedNotificationParams \{
\_meta?: \{ \[key: string]: unknown };
uri: string;
}

Parameters for a notifications/resources/updated notification.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

uri: string

The URI of the resource that has been updated. This might be a sub-resource of the one that the client actually subscribed to.

## `notifications/roots/list_changed`

### `RootsListChangedNotification`

interface RootsListChangedNotification \{
  jsonrpc: "2.0";
  method: "notifications/roots/list\_changed";
  params?: NotificationParams;
}

A notification from the client to the server, informing it that the list of roots has changed. This notification should be sent whenever the client adds, removes, or modifies any root. The server should then request an updated list of roots using the ListRootsRequest.

jsonrpc: "2.0"

method: "notifications/roots/list\_changed"

params?: NotificationParams

## `notifications/tools/list_changed`

### `ToolListChangedNotification`

interface ToolListChangedNotification \{
  jsonrpc: "2.0";
  method: "notifications/tools/list\_changed";
  params?: NotificationParams;
}

An optional notification from the server to the client, informing it that the list of tools it offers has changed. This may be issued by servers without any previous subscription from the client.

jsonrpc: "2.0"

method: "notifications/tools/list\_changed"

params?: NotificationParams

## `notifications/elicitation/complete`

### `ElicitationCompleteNotification`

interface ElicitationCompleteNotification \{
  jsonrpc: "2.0";
  method: "notifications/elicitation/complete";
  params: \{ elicitationId: string };
}

An optional notification from the server to the client, informing it of a completion of a out-of-band elicitation request.

jsonrpc: "2.0"

method: "notifications/elicitation/complete"

params: \{ elicitationId: string }

Type Declaration

elicitationId: string
The ID of the elicitation that completed.

## `ping`

### `PingRequest`

interface PingRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "ping";
  params?: RequestParams;
}

A ping, issued by either the server or the client, to check that the other party is still alive. The receiver must promptly respond, or else may be disconnected.

jsonrpc: "2.0"

id: RequestId

method: "ping"

params?: RequestParams

## `tasks`

### `CreateTaskResult`

interface CreateTaskResult \{
  \_meta?: \{ \[key: string]: unknown };
  task: Task;
  \[key: string]: unknown;
}

A response to a task-augmented request.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

task: Task

### `RelatedTaskMetadata`

interface RelatedTaskMetadata \{
taskId: string;
}

Metadata for associating messages with a task. Include this in the \_meta field under the key io.modelcontextprotocol/related-task.

taskId: string

The task identifier this message is associated with.

### `Task`

interface Task \{
  taskId: string;
  status: TaskStatus;
  statusMessage?: string;
  createdAt: string;
  lastUpdatedAt: string;
  ttl: number | null;
  pollInterval?: number;
}

Data associated with a task.

taskId: string

The task identifier.

status: TaskStatus

Current task state.

statusMessage?: string

Optional human-readable message describing the current task state. This can provide context for any status, including:

Reasons for "cancelled" status
Summaries for "completed" status
Diagnostic information for "failed" status (e.g., error details, what went wrong)

createdAt: string

ISO 8601 timestamp when the task was created.

lastUpdatedAt: string

ISO 8601 timestamp when the task was last updated.

ttl: number | null

Actual retention duration from creation in milliseconds, null for unlimited.

pollInterval?: number

Suggested polling interval in milliseconds.

### `TaskMetadata`

interface TaskMetadata \{
ttl?: number;
}

Metadata for augmenting a request with task execution. Include this in the task field of the request parameters.

ttl?: number

Requested duration in milliseconds to retain task from creation.

### `TaskStatus`

TaskStatus: "working" | "input\_required" | "completed" | "failed" | "cancelled"

The status of a task.

## `tasks/get`

### `GetTaskRequest`

interface GetTaskRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "tasks/get";
  params: \{ taskId: string };
}

A request to retrieve the state of a task.

jsonrpc: "2.0"

id: RequestId

method: "tasks/get"

params: \{ taskId: string }

Type Declaration

taskId: string
The task identifier to query.

### `GetTaskResult`

GetTaskResult: Result & Task

The response to a tasks/get request.

## `tasks/result`

### `GetTaskPayloadRequest`

interface GetTaskPayloadRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "tasks/result";
  params: \{ taskId: string };
}

A request to retrieve the result of a completed task.

jsonrpc: "2.0"

id: RequestId

method: "tasks/result"

params: \{ taskId: string }

Type Declaration

taskId: string
The task identifier to retrieve results for.

### `GetTaskPayloadResult`

interface GetTaskPayloadResult \{
\_meta?: \{ \[key: string]: unknown };
\[key: string]: unknown;
}

The response to a tasks/result request. The structure matches the result type of the original request. For example, a tools/call task would return the CallToolResult structure.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

## `tasks/list`

### `ListTasksRequest`

interface ListTasksRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  params?: PaginatedRequestParams;
  method: "tasks/list";
}

A request to retrieve a list of tasks.

jsonrpc: "2.0"

id: RequestId

params?: PaginatedRequestParams

method: "tasks/list"

### `ListTasksResult`

interface ListTasksResult \{
  \_meta?: \{ \[key: string]: unknown };
  nextCursor?: string;
  tasks: Task\[];
  \[key: string]: unknown;
}

The response to a tasks/list request.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

nextCursor?: string

An opaque token representing the pagination position after the last returned result. If present, there may be more results available.

tasks: Task\[]

## `tasks/cancel`

### `CancelTaskRequest`

interface CancelTaskRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "tasks/cancel";
  params: \{ taskId: string };
}

A request to cancel a task.

jsonrpc: "2.0"

id: RequestId

method: "tasks/cancel"

params: \{ taskId: string }

Type Declaration

taskId: string
The task identifier to cancel.

### `CancelTaskResult`

CancelTaskResult: Result & Task

The response to a tasks/cancel request.

## `prompts/get`

### `GetPromptRequest`

interface GetPromptRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "prompts/get";
  params: GetPromptRequestParams;
}

Used by the client to get a prompt provided by the server.

jsonrpc: "2.0"

id: RequestId

method: "prompts/get"

params: GetPromptRequestParams

### `GetPromptRequestParams`

interface GetPromptRequestParams \{
  \_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
  name: string;
  arguments?: \{ \[key: string]: string };
}

Parameters for a prompts/get request.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

The name of the prompt or prompt template.

arguments?: \{ \[key: string]: string }

Arguments to use for templating the prompt.

### `GetPromptResult`

interface GetPromptResult \{
  \_meta?: \{ \[key: string]: unknown };
  description?: string;
  messages: PromptMessage\[];
  \[key: string]: unknown;
}

The server's response to a prompts/get request from the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

description?: string

An optional description for the prompt.

messages: PromptMessage\[]

### `PromptMessage`

interface PromptMessage \{
role: Role;
content: ContentBlock;
}

Describes a message returned as part of a prompt.

This is similar to SamplingMessage, but also supports the embedding of resources from the MCP server.

role: Role

content: ContentBlock

## `prompts/list`

### `ListPromptsRequest`

interface ListPromptsRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  params?: PaginatedRequestParams;
  method: "prompts/list";
}

Sent from the client to request a list of prompts and prompt templates the server has.

jsonrpc: "2.0"

id: RequestId

params?: PaginatedRequestParams

method: "prompts/list"

### `ListPromptsResult`

interface ListPromptsResult \{
  \_meta?: \{ \[key: string]: unknown };
  nextCursor?: string;
  prompts: Prompt\[];
  \[key: string]: unknown;
}

The server's response to a prompts/list request from the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

nextCursor?: string

An opaque token representing the pagination position after the last returned result. If present, there may be more results available.

prompts: Prompt\[]

### `Prompt`

interface Prompt \{
  icons?: Icon\[];
  name: string;
  title?: string;
  description?: string;
  arguments?: PromptArgument\[];
  \_meta?: \{ \[key: string]: unknown };
}

A prompt or prompt template that the server offers.

icons?: Icon\[]

Optional set of sized icons that the client can display in a user interface.

Clients that support rendering icons MUST support at least the following MIME types:

image/png - PNG images (safe, universal compatibility)
image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)

Clients that support rendering icons SHOULD also support:

image/svg+xml - SVG images (scalable but requires security precautions)
image/webp - WebP images (modern, efficient format)

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

description?: string

An optional description of what this prompt provides

arguments?: PromptArgument\[]

A list of arguments to use for templating the prompt.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `PromptArgument`

interface PromptArgument \{
  name: string;
  title?: string;
  description?: string;
  required?: boolean;
}

Describes an argument that a prompt can accept.

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

description?: string

A human-readable description of the argument.

required?: boolean

Whether this argument must be provided.

## `resources/list`

### `ListResourcesRequest`

interface ListResourcesRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  params?: PaginatedRequestParams;
  method: "resources/list";
}

Sent from the client to request a list of resources the server has.

jsonrpc: "2.0"

id: RequestId

params?: PaginatedRequestParams

method: "resources/list"

### `ListResourcesResult`

interface ListResourcesResult \{
  \_meta?: \{ \[key: string]: unknown };
  nextCursor?: string;
  resources: Resource\[];
  \[key: string]: unknown;
}

The server's response to a resources/list request from the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

nextCursor?: string

An opaque token representing the pagination position after the last returned result. If present, there may be more results available.

resources: Resource\[]

### `Resource`

interface Resource \{
  icons?: Icon\[];
  name: string;
  title?: string;
  uri: string;
  description?: string;
  mimeType?: string;
  annotations?: Annotations;
  size?: number;
  \_meta?: \{ \[key: string]: unknown };
}

A known resource that the server is capable of reading.

icons?: Icon\[]

Optional set of sized icons that the client can display in a user interface.

Clients that support rendering icons MUST support at least the following MIME types:

image/png - PNG images (safe, universal compatibility)
image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)

Clients that support rendering icons SHOULD also support:

image/svg+xml - SVG images (scalable but requires security precautions)
image/webp - WebP images (modern, efficient format)

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

uri: string

The URI of this resource.

description?: string

A description of what this resource represents.

This can be used by clients to improve the LLM's understanding of available resources. It can be thought of like a "hint" to the model.

mimeType?: string

The MIME type of this resource, if known.

annotations?: Annotations

Optional annotations for the client.

size?: number

The size of the raw resource content, in bytes (i.e., before base64 encoding or any tokenization), if known.

This can be used by Hosts to display file sizes and estimate context window usage.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

## `resources/read`

### `ReadResourceRequest`

interface ReadResourceRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "resources/read";
  params: ReadResourceRequestParams;
}

Sent from the client to the server, to read a specific resource URI.

jsonrpc: "2.0"

id: RequestId

method: "resources/read"

params: ReadResourceRequestParams

### `ReadResourceRequestParams`

interface ReadResourceRequestParams \{
\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
uri: string;
}

Parameters for a resources/read request.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

uri: string

The URI of the resource. The URI can use any protocol; it is up to the server how to interpret it.

### `ReadResourceResult`

interface ReadResourceResult \{
  \_meta?: \{ \[key: string]: unknown };
  contents: (TextResourceContents | BlobResourceContents)\[];
  \[key: string]: unknown;
}

The server's response to a resources/read request from the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

contents: (TextResourceContents | BlobResourceContents)\[]

## `resources/subscribe`

### `SubscribeRequest`

interface SubscribeRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "resources/subscribe";
  params: SubscribeRequestParams;
}

Sent from the client to request resources/updated notifications from the server whenever a particular resource changes.

jsonrpc: "2.0"

id: RequestId

method: "resources/subscribe"

params: SubscribeRequestParams

### `SubscribeRequestParams`

interface SubscribeRequestParams \{
\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
uri: string;
}

Parameters for a resources/subscribe request.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

uri: string

The URI of the resource. The URI can use any protocol; it is up to the server how to interpret it.

## `resources/templates/list`

### `ListResourceTemplatesRequest`

interface ListResourceTemplatesRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  params?: PaginatedRequestParams;
  method: "resources/templates/list";
}

Sent from the client to request a list of resource templates the server has.

jsonrpc: "2.0"

id: RequestId

params?: PaginatedRequestParams

method: "resources/templates/list"

### `ListResourceTemplatesResult`

interface ListResourceTemplatesResult \{
  \_meta?: \{ \[key: string]: unknown };
  nextCursor?: string;
  resourceTemplates: ResourceTemplate\[];
  \[key: string]: unknown;
}

The server's response to a resources/templates/list request from the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

nextCursor?: string

An opaque token representing the pagination position after the last returned result. If present, there may be more results available.

resourceTemplates: ResourceTemplate\[]

### `ResourceTemplate`

interface ResourceTemplate \{
  icons?: Icon\[];
  name: string;
  title?: string;
  uriTemplate: string;
  description?: string;
  mimeType?: string;
  annotations?: Annotations;
  \_meta?: \{ \[key: string]: unknown };
}

A template description for resources available on the server.

icons?: Icon\[]

Optional set of sized icons that the client can display in a user interface.

Clients that support rendering icons MUST support at least the following MIME types:

image/png - PNG images (safe, universal compatibility)
image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)

Clients that support rendering icons SHOULD also support:

image/svg+xml - SVG images (scalable but requires security precautions)
image/webp - WebP images (modern, efficient format)

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

uriTemplate: string

A URI template (according to RFC 6570) that can be used to construct resource URIs.

description?: string

A description of what this template is for.

This can be used by clients to improve the LLM's understanding of available resources. It can be thought of like a "hint" to the model.

mimeType?: string

The MIME type for all resources that match this template. This should only be included if all resources matching this template have the same type.

annotations?: Annotations

Optional annotations for the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

## `resources/unsubscribe`

### `UnsubscribeRequest`

interface UnsubscribeRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "resources/unsubscribe";
  params: UnsubscribeRequestParams;
}

Sent from the client to request cancellation of resources/updated notifications from the server. This should follow a previous resources/subscribe request.

jsonrpc: "2.0"

id: RequestId

method: "resources/unsubscribe"

params: UnsubscribeRequestParams

### `UnsubscribeRequestParams`

interface UnsubscribeRequestParams \{
\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
uri: string;
}

Parameters for a resources/unsubscribe request.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

uri: string

The URI of the resource. The URI can use any protocol; it is up to the server how to interpret it.

## `roots/list`

### `ListRootsRequest`

interface ListRootsRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "roots/list";
  params?: RequestParams;
}

Sent from the server to request a list of root URIs from the client. Roots allow servers to ask for specific directories or files to operate on. A common example for roots is providing a set of repositories or directories a server should operate on.

This request is typically used when the server needs to understand the file system structure or access specific locations that the client has permission to read from.

jsonrpc: "2.0"

id: RequestId

method: "roots/list"

params?: RequestParams

### `ListRootsResult`

interface ListRootsResult \{
  \_meta?: \{ \[key: string]: unknown };
  roots: Root\[];
  \[key: string]: unknown;
}

The client's response to a roots/list request from the server. This result contains an array of Root objects, each representing a root directory or file that the server can operate on.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

roots: Root\[]

### `Root`

interface Root \{
  uri: string;
  name?: string;
  \_meta?: \{ \[key: string]: unknown };
}

Represents a root directory or file that the server can operate on.

uri: string

The URI identifying the root. This must start with file:// for now. This restriction may be relaxed in future versions of the protocol to allow other URI schemes.

name?: string

An optional name for the root. This can be used to provide a human-readable identifier for the root, which may be useful for display purposes or for referencing the root in other parts of the application.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

## `sampling/createMessage`

### `CreateMessageRequest`

interface CreateMessageRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "sampling/createMessage";
  params: CreateMessageRequestParams;
}

A request from the server to sample an LLM via the client. The client has full discretion over which model to select. The client should also inform the user before beginning sampling, to allow them to inspect the request (human in the loop) and decide whether to approve it.

jsonrpc: "2.0"

id: RequestId

method: "sampling/createMessage"

params: CreateMessageRequestParams

### `CreateMessageRequestParams`

interface CreateMessageRequestParams \{
  task?: TaskMetadata;
  \_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
  messages: SamplingMessage\[];
  modelPreferences?: ModelPreferences;
  systemPrompt?: string;
  includeContext?: "none" | "thisServer" | "allServers";
  temperature?: number;
  maxTokens: number;
  stopSequences?: string\[];
  metadata?: object;
  tools?: Tool\[];
  toolChoice?: ToolChoice;
}

Parameters for a sampling/createMessage request.

task?: TaskMetadata

Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

messages: SamplingMessage\[]

modelPreferences?: ModelPreferences

The server's preferences for which model to select. The client MAY ignore these preferences.

systemPrompt?: string

An optional system prompt the server wants to use for sampling. The client MAY modify or omit this prompt.

includeContext?: "none" | "thisServer" | "allServers"

A request to include context from one or more MCP servers (including the caller), to be attached to the prompt. The client MAY ignore this request.

Default is "none". Values "thisServer" and "allServers" are soft-deprecated. Servers SHOULD only use these values if the client declares ClientCapabilities.sampling.context. These values may be removed in future spec releases.

temperature?: number

maxTokens: number

The requested maximum number of tokens to sample (to prevent runaway completions).

The client MAY choose to sample fewer tokens than the requested maximum.

stopSequences?: string\[]

metadata?: object

Optional metadata to pass through to the LLM provider. The format of this metadata is provider-specific.

tools?: Tool\[]

Tools that the model may use during generation. The client MUST return an error if this field is provided but ClientCapabilities.sampling.tools is not declared.

toolChoice?: ToolChoice

Controls how the model uses tools. The client MUST return an error if this field is provided but ClientCapabilities.sampling.tools is not declared. Default is \{ mode: "auto" }.

### `CreateMessageResult`

interface CreateMessageResult \{
  \_meta?: \{ \[key: string]: unknown };
  model: string;
  stopReason?: string;
  role: Role;
  content: SamplingMessageContentBlock | SamplingMessageContentBlock\[];
  \[key: string]: unknown;
}

The client's response to a sampling/createMessage request from the server. The client should inform the user before returning the sampled message, to allow them to inspect the response (human in the loop) and decide whether to allow the server to see it.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

model: string

The name of the model that generated the message.

stopReason?: string

The reason why sampling stopped, if known.

Standard values:

"endTurn": Natural end of the assistant's turn
"stopSequence": A stop sequence was encountered
"maxTokens": Maximum token limit was reached
"toolUse": The model wants to use one or more tools

This field is an open string to allow for provider-specific stop reasons.

role: Role

content: SamplingMessageContentBlock | SamplingMessageContentBlock\[]

### `ModelHint`

interface ModelHint \{
name?: string;
}

Hints to use for model selection.

Keys not declared here are currently left unspecified by the spec and are up to the client to interpret.

name?: string

A hint for a model name.

The client SHOULD treat this as a substring of a model name; for example:

claude-3-5-sonnet should match claude-3-5-sonnet-20241022
sonnet should match claude-3-5-sonnet-20241022, claude-3-sonnet-20240229, etc.
claude should match any Claude model

The client MAY also map the string to a different provider's model name or a different model family, as long as it fills a similar niche; for example:

gemini-1.5-flash could match claude-3-haiku-20240307

### `ModelPreferences`

interface ModelPreferences \{
  hints?: ModelHint\[];
  costPriority?: number;
  speedPriority?: number;
  intelligencePriority?: number;
}

The server's preferences for model selection, requested of the client during sampling.

Because LLMs can vary along multiple dimensions, choosing the "best" model is rarely straightforward. Different models excel in different areas—some are faster but less capable, others are more capable but more expensive, and so on. This interface allows servers to express their priorities across multiple dimensions to help clients make an appropriate selection for their use case.

These preferences are always advisory. The client MAY ignore them. It is also up to the client to decide how to interpret these preferences and how to balance them against other considerations.

hints?: ModelHint\[]

Optional hints to use for model selection.

If multiple hints are specified, the client MUST evaluate them in order (such that the first match is taken).

The client SHOULD prioritize these hints over the numeric priorities, but MAY still use the priorities to select from ambiguous matches.

costPriority?: number

How much to prioritize cost when selecting a model. A value of 0 means cost is not important, while a value of 1 means cost is the most important factor.

speedPriority?: number

How much to prioritize sampling speed (latency) when selecting a model. A value of 0 means speed is not important, while a value of 1 means speed is the most important factor.

intelligencePriority?: number

How much to prioritize intelligence and capabilities when selecting a model. A value of 0 means intelligence is not important, while a value of 1 means intelligence is the most important factor.

### `SamplingMessage`

interface SamplingMessage \{
  role: Role;
  content: SamplingMessageContentBlock | SamplingMessageContentBlock\[];
  \_meta?: \{ \[key: string]: unknown };
}

Describes a message issued to or received from an LLM API.

role: Role

content: SamplingMessageContentBlock | SamplingMessageContentBlock\[]

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `ToolChoice`

interface ToolChoice \{
mode?: "none" | "required" | "auto";
}

Controls tool selection behavior for sampling requests.

mode?: "none" | "required" | "auto"

Controls the tool use ability of the model:

"auto": Model decides whether to use tools (default)
"required": Model MUST use at least one tool before completing
"none": Model MUST NOT use any tools

### `ToolResultContent`

interface ToolResultContent \{
  type: "tool\_result";
  toolUseId: string;
  content: ContentBlock\[];
  structuredContent?: \{ \[key: string]: unknown };
  isError?: boolean;
  \_meta?: \{ \[key: string]: unknown };
}

The result of a tool use, provided by the user back to the assistant.

type: "tool\_result"

toolUseId: string

The ID of the tool use this result corresponds to.

This MUST match the ID from a previous ToolUseContent.

content: ContentBlock\[]

The unstructured result content of the tool use.

This has the same format as CallToolResult.content and can include text, images, audio, resource links, and embedded resources.

structuredContent?: \{ \[key: string]: unknown }

An optional structured result object.

If the tool defined an outputSchema, this SHOULD conform to that schema.

isError?: boolean

Whether the tool use resulted in an error.

If true, the content typically describes the error that occurred. Default: false

\_meta?: \{ \[key: string]: unknown }

Optional metadata about the tool result. Clients SHOULD preserve this field when including tool results in subsequent sampling requests to enable caching optimizations.

See General fields: \_meta for notes on \_meta usage.

### `ToolUseContent`

interface ToolUseContent \{
  type: "tool\_use";
  id: string;
  name: string;
  input: \{ \[key: string]: unknown };
  \_meta?: \{ \[key: string]: unknown };
}

A request from the assistant to call a tool.

type: "tool\_use"

id: string

A unique identifier for this tool use.

This ID is used to match tool results to their corresponding tool uses.

The name of the tool to call.

input: \{ \[key: string]: unknown }

The arguments to pass to the tool, conforming to the tool's input schema.

\_meta?: \{ \[key: string]: unknown }

Optional metadata about the tool use. Clients SHOULD preserve this field when including tool uses in subsequent sampling requests to enable caching optimizations.

See General fields: \_meta for notes on \_meta usage.

## `tools/call`

### `CallToolRequest`

interface CallToolRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  method: "tools/call";
  params: CallToolRequestParams;
}

Used by the client to invoke a tool provided by the server.

jsonrpc: "2.0"

id: RequestId

method: "tools/call"

params: CallToolRequestParams

### `CallToolRequestParams`

interface CallToolRequestParams \{
  task?: TaskMetadata;
  \_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown };
  name: string;
  arguments?: \{ \[key: string]: unknown };
}

Parameters for a tools/call request.

task?: TaskMetadata

Task augmentation is subject to capability negotiation - receivers MUST declare support for task augmentation of specific request types in their capabilities.

\_meta?: \{ progressToken?: ProgressToken; \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

Type Declaration

\[key: string]: unknown
OptionalprogressToken?: ProgressToken
If specified, the caller is requesting out-of-band progress notifications for this request (as represented by notifications/progress). The value of this parameter is an opaque token that will be attached to any subsequent notifications. The receiver is not obligated to provide these notifications.

The name of the tool.

arguments?: \{ \[key: string]: unknown }

Arguments to use for the tool call.

### `CallToolResult`

interface CallToolResult \{
  \_meta?: \{ \[key: string]: unknown };
  content: ContentBlock\[];
  structuredContent?: \{ \[key: string]: unknown };
  isError?: boolean;
  \[key: string]: unknown;
}

The server's response to a tool call.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

content: ContentBlock\[]

A list of content objects that represent the unstructured result of the tool call.

structuredContent?: \{ \[key: string]: unknown }

An optional JSON object that represents the structured result of the tool call.

isError?: boolean

Whether the tool call ended in an error.

If not set, this is assumed to be false (the call was successful).

Any errors that originate from the tool SHOULD be reported inside the result object, with isError set to true, not as an MCP protocol-level error response. Otherwise, the LLM would not be able to see that an error occurred and self-correct.

However, any errors in finding the tool, an error indicating that the server does not support tool calls, or any other exceptional conditions, should be reported as an MCP error response.

## `tools/list`

### `ListToolsRequest`

interface ListToolsRequest \{
  jsonrpc: "2.0";
  id: RequestId;
  params?: PaginatedRequestParams;
  method: "tools/list";
}

Sent from the client to request a list of tools the server has.

jsonrpc: "2.0"

id: RequestId

params?: PaginatedRequestParams

method: "tools/list"

### `ListToolsResult`

interface ListToolsResult \{
  \_meta?: \{ \[key: string]: unknown };
  nextCursor?: string;
  tools: Tool\[];
  \[key: string]: unknown;
}

The server's response to a tools/list request from the client.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

nextCursor?: string

An opaque token representing the pagination position after the last returned result. If present, there may be more results available.

tools: Tool\[]

### `Tool`

interface Tool \{
  icons?: Icon\[];
  name: string;
  title?: string;
  description?: string;
  inputSchema: \{
    \$schema?: string;
    type: "object";
    properties?: \{ \[key: string]: object };
    required?: string\[];
  };
  execution?: ToolExecution;
  outputSchema?: \{
    \$schema?: string;
    type: "object";
    properties?: \{ \[key: string]: object };
    required?: string\[];
  };
  annotations?: ToolAnnotations;
  \_meta?: \{ \[key: string]: unknown };
}

Definition for a tool the client can call.

icons?: Icon\[]

Optional set of sized icons that the client can display in a user interface.

Clients that support rendering icons MUST support at least the following MIME types:

image/png - PNG images (safe, universal compatibility)
image/jpeg (and image/jpg) - JPEG images (safe, universal compatibility)

Clients that support rendering icons SHOULD also support:

image/svg+xml - SVG images (scalable but requires security precautions)
image/webp - WebP images (modern, efficient format)

Intended for programmatic or logical use, but used as a display name in past specs or fallback (if title isn't present).

title?: string

Intended for UI and end-user contexts — optimized to be human-readable and easily understood, even by those unfamiliar with domain-specific terminology.

If not provided, the name should be used for display (except for Tool, where annotations.title should be given precedence over using name, if present).

description?: string

A human-readable description of the tool.

This can be used by clients to improve the LLM's understanding of available tools. It can be thought of like a "hint" to the model.

inputSchema: \{ \$schema?: string; type: "object"; properties?: \{ \[key: string]: object }; required?: string\[]; }

A JSON Schema object defining the expected parameters for the tool.

execution?: ToolExecution

Execution-related properties for this tool.

outputSchema?: \{ \$schema?: string; type: "object"; properties?: \{ \[key: string]: object }; required?: string\[]; }

An optional JSON Schema object defining the structure of the tool's output returned in the structuredContent field of a CallToolResult.

Defaults to JSON Schema 2020-12 when no explicit \$schema is provided. Currently restricted to type: "object" at the root level.

annotations?: ToolAnnotations

Optional additional tool information.

Display name precedence order is: title, annotations.title, then name.

\_meta?: \{ \[key: string]: unknown }

See General fields: \_meta for notes on \_meta usage.

### `ToolAnnotations`

interface ToolAnnotations \{
  title?: string;
  readOnlyHint?: boolean;
  destructiveHint?: boolean;
  idempotentHint?: boolean;
  openWorldHint?: boolean;
}

Additional properties describing a Tool to clients.

NOTE: all properties in ToolAnnotations are hints. They are not guaranteed to provide a faithful description of tool behavior (including descriptive properties like title).

Clients should never make tool use decisions based on ToolAnnotations received from untrusted servers.

title?: string

A human-readable title for the tool.

readOnlyHint?: boolean

If true, the tool does not modify its environment.

Default: false

destructiveHint?: boolean

If true, the tool may perform destructive updates to its environment. If false, the tool performs only additive updates.

(This property is meaningful only when readOnlyHint == false)

Default: true

idempotentHint?: boolean

If true, calling the tool repeatedly with the same arguments will have no additional effect on its environment.

(This property is meaningful only when readOnlyHint == false)

Default: false

openWorldHint?: boolean

If true, this tool may interact with an "open world" of external entities. If false, the tool's domain of interaction is closed. For example, the world of a web search tool is open, whereas that of a memory tool is not.

Default: true

### `ToolExecution`

interface ToolExecution \{
taskSupport?: "forbidden" | "optional" | "required";
}

Execution-related properties for a tool.

taskSupport?: "forbidden" | "optional" | "required"

Indicates whether this tool supports task-augmented execution. This allows clients to handle long-running operations through polling the task system.

"forbidden": Tool does not support task-augmented execution (default when absent)
"optional": Tool may support task-augmented execution
"required": Tool requires task-augmented execution

Default: "forbidden"