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Jeremiah Lowin commited on
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Parent(s): 31e3fd3
Update docs for context
Browse files- docs/servers/context.mdx +68 -14
- docs/servers/prompts.mdx +11 -20
- docs/servers/resources.mdx +32 -22
- docs/servers/tools.mdx +35 -34
docs/servers/context.mdx
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---
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title: MCP Context
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sidebarTitle: Context
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description: Access MCP capabilities like logging, progress, and resources within your
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icon: rectangle-code
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---
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import { VersionBadge } from '/snippets/version-badge.mdx'
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When defining FastMCP [tools](/servers/tools), your functions might need to interact with the underlying MCP session or access server capabilities. FastMCP provides the `Context` object for this purpose.
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## What Is Context?
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The `Context` object provides a clean interface to access MCP features within your
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- **Logging**: Send debug, info, warning, and error messages back to the client
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- **Progress Reporting**: Update the client on the progress of long-running operations
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## Accessing the Context
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To use the context object within
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```python
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from fastmcp import FastMCP, Context
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- The parameter name (e.g., `ctx`, `context`) doesn't matter, only the type hint `Context` is important.
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- The context parameter can be placed anywhere in your function's signature.
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- The context is optional -
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- Context is only available
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- Context methods are async, so your
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## Context Capabilities
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### Logging
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Send log messages back to the MCP client. This is useful for debugging and providing visibility into
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```python
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@mcp.tool()
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**Available Logging Methods:**
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- **`ctx.debug(message: str)`**: Low-level details useful for debugging
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- **`ctx.info(message: str)`**: General information about
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- **`ctx.warning(message: str)`**: Potential issues that didn't prevent execution
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- **`ctx.error(message: str)`**: Errors that occurred during execution
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- **`ctx.log(level: Literal["debug", "info", "warning", "error"], message: str, logger_name: str | None = None)`**: Generic log method supporting custom logger names
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### Progress Reporting
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For long-running
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```python
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@mcp.tool()
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### Resource Access
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Read data from resources registered with your FastMCP server. This allows
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```python
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@mcp.tool()
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<VersionBadge version="2.0.0" />
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Request the client's LLM to generate text based on provided messages. This is useful when your
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```python
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@mcp.tool()
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Direct use of `session` or `request_context` requires understanding the low-level MCP Python SDK and may be less stable than using the methods provided directly on the `Context` object.
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</Warning>
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## Using Context in
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---
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title: MCP Context
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sidebarTitle: Context
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description: Access MCP capabilities like logging, progress, and resources within your MCP objects.
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icon: rectangle-code
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---
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import { VersionBadge } from '/snippets/version-badge.mdx'
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When defining FastMCP [tools](/servers/tools), [resources](/servers/resources), resource templates, or [prompts](/servers/prompts), your functions might need to interact with the underlying MCP session or access server capabilities. FastMCP provides the `Context` object for this purpose.
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## What Is Context?
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The `Context` object provides a clean interface to access MCP features within your functions, including:
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- **Logging**: Send debug, info, warning, and error messages back to the client
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- **Progress Reporting**: Update the client on the progress of long-running operations
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## Accessing the Context
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To use the context object within any of your functions, simply add a parameter to your function signature and type-hint it as `Context`. FastMCP will automatically inject the context instance when your function is called.
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```python
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from fastmcp import FastMCP, Context
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- The parameter name (e.g., `ctx`, `context`) doesn't matter, only the type hint `Context` is important.
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- The context parameter can be placed anywhere in your function's signature.
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- The context is optional - functions that don't need it can omit the parameter.
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- Context is only available during a request; attempting to use context methods outside a request will raise errors.
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- Context methods are async, so your function usually needs to be async as well.
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## Context Capabilities
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### Logging
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Send log messages back to the MCP client. This is useful for debugging and providing visibility into function execution during a request.
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```python
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@mcp.tool()
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**Available Logging Methods:**
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- **`ctx.debug(message: str)`**: Low-level details useful for debugging
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- **`ctx.info(message: str)`**: General information about execution
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- **`ctx.warning(message: str)`**: Potential issues that didn't prevent execution
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- **`ctx.error(message: str)`**: Errors that occurred during execution
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- **`ctx.log(level: Literal["debug", "info", "warning", "error"], message: str, logger_name: str | None = None)`**: Generic log method supporting custom logger names
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### Progress Reporting
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For long-running operations, notify the client about the progress. This allows clients to display progress indicators and provide a better user experience.
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```python
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@mcp.tool()
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### Resource Access
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Read data from resources registered with your FastMCP server. This allows functions to access files, configuration, or dynamically generated content.
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```python
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@mcp.tool()
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<VersionBadge version="2.0.0" />
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Request the client's LLM to generate text based on provided messages. This is useful when your function needs to leverage the LLM's capabilities to process data or generate responses.
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```python
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@mcp.tool()
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Direct use of `session` or `request_context` requires understanding the low-level MCP Python SDK and may be less stable than using the methods provided directly on the `Context` object.
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</Warning>
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## Using Context in Different Components
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All FastMCP components (tools, resources, templates, and prompts) can use the Context object following the same pattern - simply add a parameter with the `Context` type annotation.
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### Context in Resources and Templates
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Resources and resource templates can access context to customize their behavior:
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```python
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@mcp.resource("resource://user-data")
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async def get_user_data(ctx: Context) -> dict:
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"""Fetch personalized user data based on the request context."""
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user_id = ctx.client_id or "anonymous"
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await ctx.info(f"Fetching data for user {user_id}")
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# Example of using context for dynamic resource generation
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return {
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"user_id": user_id,
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"last_access": datetime.now().isoformat(),
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"request_id": ctx.request_id
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}
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@mcp.resource("resource://users/{user_id}/profile")
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async def get_user_profile(user_id: str, ctx: Context) -> dict:
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"""Fetch user profile from database with context-aware logging."""
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await ctx.info(f"Fetching profile for user {user_id}")
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# Example of using context in a template resource
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# In a real implementation, you might query a database
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return {
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"id": user_id,
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"name": f"User {user_id}",
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"request_id": ctx.request_id
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}
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```
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### Context in Prompts
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Prompts can use context to generate more dynamic templates:
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```python
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@mcp.prompt()
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async def data_analysis_request(dataset: str, ctx: Context) -> str:
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"""Generate a request to analyze data with contextual information."""
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await ctx.info(f"Generating data analysis prompt for {dataset}")
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# Could use context to read configuration or personalize the prompt
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return f"""Please analyze the following dataset: {dataset}
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Request initiated at: {datetime.now().isoformat()}
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Request ID: {ctx.request_id}
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"""
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```
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<VersionBadge version="2.3.0" />
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All FastMCP objects now support context injection using the same consistent pattern, making it easy to add session-aware capabilities to all aspects of your MCP server.
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docs/servers/prompts.mdx
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Use `async def` when your prompt function performs I/O operations like network requests, database queries, file I/O, or external service calls.
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###
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```
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@mcp.prompt()
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async def generate_report_request(report_type: str, ctx: Context) -> str:
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"""Generates a request for a report
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await ctx.info(f"Generating prompt for report type: {report_type}")
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# Could potentially use ctx.read_resource to fetch data
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# Or ctx.sample to get additional input from the LLM
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return f"Please create a {report_type} report based on the available data."
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```
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- **Logging:** `ctx.debug()`, `ctx.info()`, etc.
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- **Resource Access:** `ctx.read_resource(uri)`
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- **LLM Sampling:** `ctx.sample(...)`
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- **Request Info:** `ctx.request_id`, `ctx.client_id`
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Refer to the [Context documentation](/servers/context) for more details on these capabilities.
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## Server Behavior
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Use `async def` when your prompt function performs I/O operations like network requests, database queries, file I/O, or external service calls.
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### Accessing MCP Context
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<VersionBadge version="2.2.5" />
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Prompts can access additional MCP information and features through the `Context` object. To access it, add a parameter to your prompt function with a type annotation of `Context`:
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```python {6}
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from fastmcp import FastMCP, Context
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mcp = FastMCP(name="PromptServer")
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@mcp.prompt()
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async def generate_report_request(report_type: str, ctx: Context) -> str:
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"""Generates a request for a report."""
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return f"Please create a {report_type} report. Request ID: {ctx.request_id}"
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```
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For full documentation on the Context object and all its capabilities, see the [Context documentation](/servers/context).
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## Server Behavior
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docs/servers/resources.mdx
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- **`mime_type`**: Specifies the content type (FastMCP often infers a default like `text/plain` or `application/json`, but explicit is better for non-text types).
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- **`tags`**: A set of strings for categorization, potentially used by clients for filtering.
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### Asynchronous Resources
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Resource Templates allow clients to request resources whose content depends on parameters embedded in the URI. Define a template using the **same `@mcp.resource` decorator**, but include `{parameter_name}` placeholders in the URI string and add corresponding arguments to your function signature.
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Resource templates generate a new resource for each unique set of parameters, which means that resources can be dynamically created on-demand. For example, if the resource template `"user://profile/{name}"` is registered, MCP clients could request `"user://profile/ford"` or `"user://profile/marvin"` to retrieve either of those two user profiles as resources, without having to register each resource individually.
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Here is a complete example that shows how to define two resource templates:
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Templates provide a powerful way to expose parameterized data access points following REST-like principles.
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### Custom Template Keys
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<VersionBadge version="2.2.0" />
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Similar to resources, you can provide custom keys when directly adding templates:
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```python
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from fastmcp.resources import ResourceTemplate
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# Create a template with a function
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template = ResourceTemplate.from_function(
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my_function,
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uri_template="data://{id}/details",
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name="Data Details"
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)
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# Register with a custom key
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mcp._resource_manager.add_template(template, key="custom://{id}/view")
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```
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This allows accessing the same template implementation through different URI patterns.
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## Server Behavior
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### Duplicate Resources
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- **`mime_type`**: Specifies the content type (FastMCP often infers a default like `text/plain` or `application/json`, but explicit is better for non-text types).
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- **`tags`**: A set of strings for categorization, potentially used by clients for filtering.
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### Accessing MCP Context
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<VersionBadge version="2.2.5" />
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Resources and resource templates can access additional MCP information and features through the `Context` object. To access it, add a parameter to your resource function with a type annotation of `Context`:
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```python {6, 14}
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from fastmcp import FastMCP, Context
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mcp = FastMCP(name="DataServer")
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@mcp.resource("resource://system-status")
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async def get_system_status(ctx: Context) -> dict:
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"""Provides system status information."""
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return {
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"status": "operational",
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"request_id": ctx.request_id
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}
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@mcp.resource("resource://{name}/details")
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async def get_details(name: str, ctx: Context) -> dict:
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"""Get details for a specific name."""
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return {
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"name": name,
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"accessed_at": ctx.request_id
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}
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```
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For full documentation on the Context object and all its capabilities, see the [Context documentation](/servers/context).
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### Asynchronous Resources
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Resource Templates allow clients to request resources whose content depends on parameters embedded in the URI. Define a template using the **same `@mcp.resource` decorator**, but include `{parameter_name}` placeholders in the URI string and add corresponding arguments to your function signature.
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Resource templates share most configuration options with regular resources (name, description, mime_type, tags), but add the ability to define URI parameters that map to function parameters.
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Resource templates generate a new resource for each unique set of parameters, which means that resources can be dynamically created on-demand. For example, if the resource template `"user://profile/{name}"` is registered, MCP clients could request `"user://profile/ford"` or `"user://profile/marvin"` to retrieve either of those two user profiles as resources, without having to register each resource individually.
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Here is a complete example that shows how to define two resource templates:
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Templates provide a powerful way to expose parameterized data access points following REST-like principles.
|
| 413 |
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| 414 |
## Server Behavior
|
| 415 |
|
| 416 |
### Duplicate Resources
|
docs/servers/tools.mdx
CHANGED
|
@@ -263,7 +263,8 @@ FastMCP automatically catches exceptions raised within your tool function:
|
|
| 263 |
|
| 264 |
Using informative exceptions helps the LLM understand failures and react appropriately.
|
| 265 |
|
| 266 |
-
##
|
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|
| 267 |
|
| 268 |
Tools can access MCP features like logging, reading resources, or reporting progress through the `Context` object. To use it, add a parameter to your tool function with the type hint `Context`.
|
| 269 |
|
|
@@ -304,39 +305,6 @@ The Context object provides access to:
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|
| 304 |
|
| 305 |
For full documentation on the Context object and all its capabilities, see the [Context documentation](/servers/context).
|
| 306 |
|
| 307 |
-
## Server Behavior
|
| 308 |
-
|
| 309 |
-
### Duplicate Tools
|
| 310 |
-
|
| 311 |
-
<VersionBadge version="2.1.0" />
|
| 312 |
-
|
| 313 |
-
You can control how the FastMCP server behaves if you try to register multiple tools with the same name. This is configured using the `on_duplicate_tools` argument when creating the `FastMCP` instance.
|
| 314 |
-
|
| 315 |
-
```python
|
| 316 |
-
from fastmcp import FastMCP
|
| 317 |
-
|
| 318 |
-
mcp = FastMCP(
|
| 319 |
-
name="StrictServer",
|
| 320 |
-
# Configure behavior for duplicate tool names
|
| 321 |
-
on_duplicate_tools="error"
|
| 322 |
-
)
|
| 323 |
-
|
| 324 |
-
@mcp.tool()
|
| 325 |
-
def my_tool(): return "Version 1"
|
| 326 |
-
|
| 327 |
-
# This will now raise a ValueError because 'my_tool' already exists
|
| 328 |
-
# and on_duplicate_tools is set to "error".
|
| 329 |
-
# @mcp.tool()
|
| 330 |
-
# def my_tool(): return "Version 2"
|
| 331 |
-
```
|
| 332 |
-
|
| 333 |
-
The duplicate behavior options are:
|
| 334 |
-
|
| 335 |
-
- `"warn"` (default): Logs a warning and the new tool replaces the old one.
|
| 336 |
-
- `"error"`: Raises a `ValueError`, preventing the duplicate registration.
|
| 337 |
-
- `"replace"`: Silently replaces the existing tool with the new one.
|
| 338 |
-
- `"ignore"`: Keeps the original tool and ignores the new registration attempt.
|
| 339 |
-
|
| 340 |
## Parameter Types
|
| 341 |
|
| 342 |
FastMCP supports a wide variety of parameter types to give you flexibility when designing your tools.
|
|
@@ -663,3 +631,36 @@ Common validation options include:
|
|
| 663 |
| `description` | Any | Human-readable description (appears in schema) |
|
| 664 |
|
| 665 |
When a client sends invalid data, FastMCP will return a validation error explaining why the parameter failed validation.
|
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|
| 263 |
|
| 264 |
Using informative exceptions helps the LLM understand failures and react appropriately.
|
| 265 |
|
| 266 |
+
## MCP Context
|
| 267 |
+
|
| 268 |
|
| 269 |
Tools can access MCP features like logging, reading resources, or reporting progress through the `Context` object. To use it, add a parameter to your tool function with the type hint `Context`.
|
| 270 |
|
|
|
|
| 305 |
|
| 306 |
For full documentation on the Context object and all its capabilities, see the [Context documentation](/servers/context).
|
| 307 |
|
|
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|
|
|
|
| 308 |
## Parameter Types
|
| 309 |
|
| 310 |
FastMCP supports a wide variety of parameter types to give you flexibility when designing your tools.
|
|
|
|
| 631 |
| `description` | Any | Human-readable description (appears in schema) |
|
| 632 |
|
| 633 |
When a client sends invalid data, FastMCP will return a validation error explaining why the parameter failed validation.
|
| 634 |
+
|
| 635 |
+
## Server Behavior
|
| 636 |
+
|
| 637 |
+
### Duplicate Tools
|
| 638 |
+
|
| 639 |
+
<VersionBadge version="2.1.0" />
|
| 640 |
+
|
| 641 |
+
You can control how the FastMCP server behaves if you try to register multiple tools with the same name. This is configured using the `on_duplicate_tools` argument when creating the `FastMCP` instance.
|
| 642 |
+
|
| 643 |
+
```python
|
| 644 |
+
from fastmcp import FastMCP
|
| 645 |
+
|
| 646 |
+
mcp = FastMCP(
|
| 647 |
+
name="StrictServer",
|
| 648 |
+
# Configure behavior for duplicate tool names
|
| 649 |
+
on_duplicate_tools="error"
|
| 650 |
+
)
|
| 651 |
+
|
| 652 |
+
@mcp.tool()
|
| 653 |
+
def my_tool(): return "Version 1"
|
| 654 |
+
|
| 655 |
+
# This will now raise a ValueError because 'my_tool' already exists
|
| 656 |
+
# and on_duplicate_tools is set to "error".
|
| 657 |
+
# @mcp.tool()
|
| 658 |
+
# def my_tool(): return "Version 2"
|
| 659 |
+
```
|
| 660 |
+
|
| 661 |
+
The duplicate behavior options are:
|
| 662 |
+
|
| 663 |
+
- `"warn"` (default): Logs a warning and the new tool replaces the old one.
|
| 664 |
+
- `"error"`: Raises a `ValueError`, preventing the duplicate registration.
|
| 665 |
+
- `"replace"`: Silently replaces the existing tool with the new one.
|
| 666 |
+
- `"ignore"`: Keeps the original tool and ignores the new registration attempt.
|