April 30, 2025

FastMCP Context Switching

Seamless access for all components

AIOSSFastMCP
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FastMCP Context Switching

Previously in FastMCP, the powerful Context object – the gateway to MCP features like logging, progress reporting, resource access, and client LLM sampling – was only easily accessible in MCP tool functions. While tools are central to MCP, this limited where you could add dynamic, session-aware logic.

Starting with FastMCP 2.2.5, the Context object is now available across all FastMCP components! You can now seamlessly inject and use context within:

  • Tools (@tool())
  • Resources (@resource("resource://user"))
  • Resource templates (e.g., @resource("resource://users/{user_id}"))
  • Prompt functions (@prompt())

In all cases, the pattern is the same: add a keyword argument to your decorated function and give it a type hint of Context. FastMCP will detect the annotation and inject the correct context automatically.

from fastmcp import FastMCP, Context


mcp = FastMCP(name="ContextDemo")


@mcp.tool()
async def add(a: int, b: int, ctx: Context) -> int:
    # ctx will be automatically injected by FastMCP
    await ctx.debug(f"Adding {a} and {b}")
    return a + b

In addition to logging, Context allows you to take advantage of powerful features like client LLM sampling.

For more details, see the FastMCP Context documentation.

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