v1.3.0

Python SDK 1.3.0 - 2025-02-20

Breaking Changes

• Context API Changes: The Context logging methods (info, debug, warning, error) are now async and must be awaited. (#172)

New Features

Lifespan Support

Added comprehensive server lifecycle management through the lifespan API:

@dataclass
class AppContext:
    db: Database

@asynccontextmanager
async def app_lifespan(server: FastMCP) -> AsyncIterator[AppContext]:
    try:
        await db.connect()
        yield AppContext(db=db)
    finally:
        await db.disconnect()

mcp = FastMCP("My App", lifespan=app_lifespan)

@mcp.tool()
def query_db(ctx: Context) -> str:
    db = ctx.request_context.lifespan_context["db"]
    return db.query()

(#203)

Async Resources

Added support for async resource functions in FastMCP:

@mcp.resource("users://{user_id}")
async def get_user(user_id: str) -> str:
    async with client.session() as session:
        response = await session.get(f"/users/{user_id}")
        return await response.text()

(#157)

Concurrent Request Handling

Made message handling concurrent, allowing multiple requests to be processed simultaneously. (#206)

Request Cancellation

Added support for canceling in-flight requests and cleaning up resources. (#167)

Server Instructions

Added support for the instructions field in server initialization, allowing servers to provide usage guidance. (#150)

Bug Fixes

• Fixed progress reporting for first tool call by correcting progress_token handling (#176)
• Fixed server crash when using debug logging (#158)
• Fixed resource template handling in FastMCP server (#137)
• Fixed MIME type preservation in resource responses (#170)
• Fixed documentation for environment variables in CLI commands (#149)
• Fixed request ID preservation in JSON-RPC responses (#205)

Dependency Updates

• Relaxed version constraints for better compatibility:
  • pydantic: Changed from >=2.10.1,<3.0.0 to >=2.7.2,<3.0.0
  • pydantic-settings: Changed from >=2.6.1 to >=2.5.2
  • uvicorn: Changed from >=0.30 to >=0.23.1
    (#180)

Examples

• Added a simple chatbot example client to demonstrate SDK usage (#98)

Client Improvements

• Added client support for sampling, list roots, and ping requests (#218)
• Added flexible type system for tool result returns (#222)

Compatibility and Platform Support

• Updated URL validation to allow file and other nonstandard schemas (#68fcf92)
• Force stdin/stdout encoding to UTF-8 for cross-platform compatibility (#d92ee8f)

Internal Improvements

• Improved type annotations for better IDE support (#181)
• Added comprehensive tests for SSE transport (#151)
• Updated types to match 2024-11-05 MCP schema (#165)
• Refactored request and notification handling for better code organization (#166)

New Contributors

• @salman1993 made their first contribution in #150
• @micpst made their first contribution in #158
• @3choff made their first contribution in #98
• @cr7258 made their first contribution in #149
• @sheffler made their first contribution in #172
• @jeremydanielfox made their first contribution in #180
• @zzstoatzz made their first contribution in #181

Full Changelog: v1.2.1...v1.3.0