switch from `pyright` to `ty` (#1545)

.github/workflows/marvin.yml

@@ -70,6 +70,6 @@ jobs:
           mode: tag
           trigger_phrase: "/marvin"
           allowed_bots: "*"
-          allowed_tools: "WebSearch,WebFetch,Bash(uv:*),Bash(pre-commit:*),Bash(pytest:*),Bash(ruff:*),Bash(pyright:*),Bash(git:*),Bash(gh:*),mcp__github__add_issue_comment,mcp__github__create_issue,mcp__github__get_issue,mcp__github__list_issues,mcp__github__search_issues,mcp__github__update_issue,mcp__github__update_issue_comment,mcp__github__create_pull_request,mcp__github__get_pull_request,mcp__github__get_pull_request_comments,mcp__github__get_pull_request_files,mcp__github__get_pull_request_reviews,mcp__github__get_pull_request_status,mcp__github__list_pull_requests,mcp__github__update_pull_request,mcp__github__update_pull_request_branch,mcp__github__update_pull_request_comment,mcp__github__merge_pull_request"
+          allowed_tools: "WebSearch,WebFetch,Bash(uv:*),Bash(pre-commit:*),Bash(pytest:*),Bash(ruff:*),Bash(ty:*),Bash(git:*),Bash(gh:*),mcp__github__add_issue_comment,mcp__github__create_issue,mcp__github__get_issue,mcp__github__list_issues,mcp__github__search_issues,mcp__github__update_issue,mcp__github__update_issue_comment,mcp__github__create_pull_request,mcp__github__get_pull_request,mcp__github__get_pull_request_comments,mcp__github__get_pull_request_files,mcp__github__get_pull_request_reviews,mcp__github__get_pull_request_status,mcp__github__list_pull_requests,mcp__github__update_pull_request,mcp__github__update_pull_request_branch,mcp__github__update_pull_request_comment,mcp__github__merge_pull_request"
           additional_permissions: |
             actions: read

.github/workflows/run-static.yml

@@ -36,12 +36,9 @@ jobs:
         with:
           enable-cache: true
           cache-dependency-glob: "uv.lock"
-      - name: Set up Python
-        uses: actions/setup-python@v5
-        with:
-          python-version: "3.12"
+
       - name: Install dependencies
-        run: uv sync --dev
+        run: uv sync
       - name: Check lockfile is up to date
         run: |
           if ! uv lock --check; then
@@ -51,6 +48,6 @@ jobs:
           fi
           echo "✅ Lockfile is up to date"
       - name: Run pre-commit
-        uses: pre-commit/action@v3.0.1
+        run: uv run pre-commit run --all-files
         env:
           SKIP: no-commit-to-branch

.pre-commit-config.yaml

@@ -22,11 +22,16 @@ repos:
       # Run the formatter.
       - id: ruff-format
 
-  - repo: https://github.com/northisup/pyright-pretty
-    rev: v0.1.0
+  - repo: local
     hooks:
-      - id: pyright-pretty
+      - id: ty
+        name: type check
+        entry: ty check
+        language: system
+        types: [python]
         files: ^src/|^tests/
+        pass_filenames: false
+        require_serial: true
 
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v4.3.0

AGENTS.md

@@ -10,7 +10,7 @@ FastMCP is a comprehensive Python framework (Python ≥3.10) for building Model
 
 ```bash
 uv sync                              # Install dependencies
-uv run pre-commit run --all-files    # Ruff + Prettier + Pyright
+uv run pre-commit run --all-files    # Ruff + Prettier + ty
 uv run pytest                        # Run full test suite
 ```
 
@@ -222,7 +222,7 @@ uv sync                    # Installs all deps including dev tools
 ### Validation Commands (Run Frequently)
 
 - **Linting**: `uv run ruff check` (or with `--fix`)
-- **Type Checking**: `uv run pyright`
+- **Type Checking**: `uv run ty check`
 - **All Checks**: `uv run pre-commit run --all-files`
 
 ### Testing
@@ -247,5 +247,5 @@ uv sync                    # Installs all deps including dev tools
 
 1. **Dependencies**: Always `uv sync` first
 2. **Pre-commit fails**: Run `uv run pre-commit run --all-files` to see failures
-3. **Type errors**: Use `uv run pyright` directly, check `pyproject.toml` config
+3. **Type errors**: Use `uv run ty check` directly, check `pyproject.toml` config
 4. **Test timeouts**: Default 3s - optimize or mark as integration tests

justfile

@@ -6,9 +6,9 @@ build:
 test: build
     uv run --frozen pytest -xvs tests
 
-# Run pyright on all files
+# Run ty type checker on all files
 typecheck:
-    uv run --frozen pyright
+    uv run --frozen ty check
 
 # Serve documentation locally
 docs:

pyproject.toml

@@ -50,7 +50,7 @@ dev = [
     "psutil",
     "pyinstrument>=5.0.2",
     "pyperclip>=1.9.0",
-    "pyright>=1.1.389",
+    "ty>=0.0.1a19",
     "pytest>=8.3.3",
     "pytest-asyncio>=0.23.5",
     "pytest-cov>=6.1.1",
@@ -114,18 +114,23 @@ python_files = ["test_*.py", "*_test.py"]
 python_classes = ["Test*"]
 python_functions = ["test_*"]
 
-[tool.pyright]
+[tool.ty.src]
 include = ["src", "tests"]
 exclude = ["**/node_modules", "**/__pycache__", ".venv", ".git", "dist"]
-pythonVersion = "3.10"
-pythonPlatform = "Darwin"
-typeCheckingMode = "basic"
-reportMissingImports = true
-reportMissingTypeStubs = false
-useLibraryCodeForTypes = true
-venvPath = "."
-venv = ".venv"
-strict = ["src/fastmcp/server/server.py"]
+
+[tool.ty.environment]
+python-version = "3.10"
+
+[tool.ty.rules]
+# Rules with too many errors to fix right now (40+ each)
+invalid-argument-type = "ignore" # 40 errors
+no-matching-overload = "ignore"  # 126 errors  
+unknown-argument = "ignore"      # 61 errors
+unresolved-attribute = "ignore"  # 60 errors
+
+# Rules with moderate errors that need more investigation
+call-non-callable = "ignore" # 7 errors
+missing-argument = "ignore"  # 23 errors
 
 [tool.ruff.lint]
 extend-select = ["I", "UP"]

src/fastmcp/cli/run.py

@@ -107,7 +107,7 @@ async def import_server(file: Path, server_or_factory: str | None = None) -> Any
         sys.exit(1)
 
     # Handle module:object syntax
-    if ":" in server_or_factory:
+    if server_or_factory and ":" in server_or_factory:
         module_name, object_name = server_or_factory.split(":", 1)
         try:
             server_module = importlib.import_module(module_name)

src/fastmcp/experimental/utilities/openapi/parser.py

@@ -549,7 +549,11 @@ class OpenAPIParser(
                         return
 
                     # Add this schema and recursively find its dependencies
-                    if schema_name not in collected and schema_name in all_schemas:
+                    if (
+                        collected is not None
+                        and schema_name not in collected
+                        and schema_name in all_schemas
+                    ):
                         collected.add(schema_name)
                         # Recursively find dependencies of this schema
                         find_refs(all_schemas[schema_name])

src/fastmcp/server/context.py

@@ -44,7 +44,7 @@ from fastmcp.utilities.types import get_cached_typeadapter
 logger = get_logger(__name__)
 
 T = TypeVar("T")
-_current_context: ContextVar[Context | None] = ContextVar("context", default=None)
+_current_context: ContextVar[Context | None] = ContextVar("context", default=None)  # type: ignore[assignment]
 _flush_lock = asyncio.Lock()
 
 

src/fastmcp/server/http.py

@@ -64,7 +64,7 @@ class StreamableHTTPASGIApp:
                 raise
 
 
-_current_http_request: ContextVar[Request | None] = ContextVar(
+_current_http_request: ContextVar[Request | None] = ContextVar(  # type: ignore[assignment]
     "http_request",
     default=None,
 )

src/fastmcp/tools/tool_transform.py

@@ -29,7 +29,7 @@ logger = get_logger(__name__)
 
 
 # Context variable to store current transformed tool
-_current_tool: ContextVar[TransformedTool | None] = ContextVar(
+_current_tool: ContextVar[TransformedTool | None] = ContextVar(  # type: ignore[assignment]
     "_current_tool", default=None
 )
 

tests/client/test_elicitation.py

@@ -547,6 +547,8 @@ class TestPatternMatching:
                     return "You declined"
                 case CancelledElicitation():
                     return "Cancelled"
+                case _:
+                    return "Unknown result"
 
         async def elicitation_handler(message, response_type, params, ctx):
             return ElicitResult(action="accept", content={"value": "Alice"})
@@ -570,6 +572,8 @@ class TestPatternMatching:
                     return "You declined"
                 case CancelledElicitation():
                     return "Cancelled"
+                case _:
+                    return "Unknown result"
 
         async def elicitation_handler(message, response_type, params, ctx):
             return ElicitResult(action="decline")
@@ -593,6 +597,8 @@ class TestPatternMatching:
                     return "You declined"
                 case CancelledElicitation():
                     return "Cancelled"
+                case _:
+                    return "Unknown result"
 
         async def elicitation_handler(message, response_type, params, ctx):
             return ElicitResult(action="cancel")

tests/integration_tests/auth/test_github_provider_integration.py

@@ -116,7 +116,7 @@ def create_github_server_with_mock_callback(
         separator = "&" if "?" in str(params.redirect_uri) else "?"
         return f"{params.redirect_uri}{separator}{urlencode(callback_params)}"
 
-    auth.authorize = mock_authorize
+    auth.authorize = mock_authorize  # type: ignore[assignment]
 
     # Mock the token verifier to accept our fake tokens
     original_verify_token = auth._token_validator.verify_token
@@ -137,7 +137,7 @@ def create_github_server_with_mock_callback(
         # Fall back to original verification for other tokens
         return await original_verify_token(token)
 
-    auth._token_validator.verify_token = mock_verify_token
+    auth._token_validator.verify_token = mock_verify_token  # type: ignore[assignment]
 
     # Create FastMCP server with mocked GitHub authentication
     server = FastMCP("GitHub OAuth Integration Test Server (Mock)", auth=auth)

uv.lock

@@ -558,7 +558,6 @@ dev = [
     { name = "psutil" },
     { name = "pyinstrument" },
     { name = "pyperclip" },
-    { name = "pyright" },
     { name = "pytest" },
     { name = "pytest-asyncio" },
     { name = "pytest-cov" },
@@ -569,6 +568,7 @@ dev = [
     { name = "pytest-timeout" },
     { name = "pytest-xdist" },
     { name = "ruff" },
+    { name = "ty" },
 ]
 
 [package.metadata]
@@ -599,7 +599,6 @@ dev = [
     { name = "psutil" },
     { name = "pyinstrument", specifier = ">=5.0.2" },
     { name = "pyperclip", specifier = ">=1.9.0" },
-    { name = "pyright", specifier = ">=1.1.389" },
     { name = "pytest", specifier = ">=8.3.3" },
     { name = "pytest-asyncio", specifier = ">=0.23.5" },
     { name = "pytest-cov", specifier = ">=6.1.1" },
@@ -610,6 +609,7 @@ dev = [
     { name = "pytest-timeout", specifier = ">=2.4.0" },
     { name = "pytest-xdist", specifier = ">=3.6.1" },
     { name = "ruff" },
+    { name = "ty", specifier = ">=0.0.1a19" },
 ]
 
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 ]
 
-[[package]]
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-version = "1.1.403"
-source = { registry = "https://pypi.org/simple" }
-dependencies = [
-    { name = "nodeenv" },
-    { name = "typing-extensions" },
-]
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-wheels = [
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-]
-
 [[package]]
 name = "pytest"
 version = "8.4.1"
@@ -2101,6 +2088,31 @@ wheels = [
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 ]
 
+[[package]]
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+version = "0.0.1a19"
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