MCP Context
Access MCP capabilities like logging, progress, and resources within your MCP objects.
When defining FastMCP tools, resources, resource templates, or prompts, your functions might need to interact with the underlying MCP session or access advanced server capabilities. FastMCP provides the Context
object for this purpose.
What Is Context?
The Context
object provides a clean interface to access MCP features within your functions, including:
- Logging: Send debug, info, warning, and error messages back to the client
- Progress Reporting: Update the client on the progress of long-running operations
- Resource Access: Read data from resources registered with the server
- LLM Sampling: Request the client’s LLM to generate text based on provided messages
- User Elicitation: Request structured input from users during tool execution
- Request Information: Access metadata about the current request
- Server Access: When needed, access the underlying FastMCP server instance
Accessing the Context
Via Dependency Injection
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.
Key Points:
- The parameter name (e.g.,
ctx
,context
) doesn’t matter, only the type hintContext
is important. - The context parameter can be placed anywhere in your function’s signature; it will not be exposed to MCP clients as a valid parameter.
- The context is optional - functions that don’t need it can omit the parameter entirely.
- Context methods are async, so your function usually needs to be async as well.
- The type hint can be a union (
Context | None
) or useAnnotated[]
and it will still work properly. - Context is only available during a request; attempting to use context methods outside a request will raise errors. If you need to debug or call your context methods outside of a request, you can type your variable as
Context | None=None
to avoid missing argument errors.
Tools
Resources and Templates
New in version: 2.2.5
Prompts
New in version: 2.2.5
Via Dependency Function
New in version: 2.2.11
While the simplest way to access context is through function parameter injection as shown above, there are cases where you need to access the context in code that may not be easy to modify to accept a context parameter, or that is nested deeper within your function calls.
FastMCP provides dependency functions that allow you to retrieve the active context from anywhere within a server request’s execution flow:
Important Notes:
- The
get_context
function should only be used within the context of a server request. Calling it outside of a request will raise aRuntimeError
. - The
get_context
function is server-only and should not be used in client code.
Context Capabilities
FastMCP provides several advanced capabilities through the context object. Each capability has dedicated documentation with comprehensive examples and best practices:
Logging
Send debug, info, warning, and error messages back to the MCP client for visibility into function execution.
See Server Logging for complete documentation and examples.
Client Elicitation
New in version: 2.10.0
Request structured input from clients during tool execution, enabling interactive workflows and progressive disclosure. This is a new feature in the 6/18/2025 MCP spec.
See User Elicitation for detailed examples and supported response types.
LLM Sampling
New in version: 2.0.0
Request the client’s LLM to generate text based on provided messages, useful for leveraging AI capabilities within your tools.
See LLM Sampling for comprehensive usage and advanced techniques.
Progress Reporting
Update clients on the progress of long-running operations, enabling progress indicators and better user experience.
See Progress Reporting for detailed patterns and examples.
Resource Access
Read data from resources registered with your FastMCP server, allowing access to files, configuration, or dynamic content.
Method signature:
ctx.read_resource(uri: str | AnyUrl) -> list[ReadResourceContents]
: Returns a list of resource content parts
Change Notifications
New in version: 2.9.1
FastMCP automatically sends list change notifications when components (such as tools, resources, or prompts) are added, removed, enabled, or disabled. In rare cases where you need to manually trigger these notifications, you can use the context methods:
These methods are primarily used internally by FastMCP’s automatic notification system and most users will not need to invoke them directly.
FastMCP Server
To access the underlying FastMCP server instance, you can use the ctx.fastmcp
property:
MCP Request
Access metadata about the current request and client.
Available Properties:
ctx.request_id -> str
: Get the unique ID for the current MCP requestctx.client_id -> str | None
: Get the ID of the client making the request, if provided during initializationctx.session_id -> str | None
: Get the MCP session ID for session-based data sharing (HTTP transports only)
The MCP request is part of the low-level MCP SDK and intended for advanced use cases. Most users will not need to use it directly.