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
- State Management: Store and share data across middleware and tool calls within a request
- 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 hint Context 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 use Annotated[] 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.
from fastmcp import FastMCP, Context
mcp = FastMCP(name="Context Demo")
@mcp.tool
async def process_file(file_uri: str, ctx: Context) -> str:
"""Processes a file, using context for logging and resource access."""
# Context is available as the ctx parameter
return "Processed file"
Resources and Templates
New in version: 2.2.5
from fastmcp import FastMCP, Context
mcp = FastMCP(name="Context Demo")
@mcp.resource("resource://user-data")
async def get_user_data(ctx: Context) -> dict:
"""Fetch personalized user data based on the request context."""
# Context is available as the ctx parameter
return {"user_id": "example"}
@mcp.resource("resource://users/{user_id}/profile")
async def get_user_profile(user_id: str, ctx: Context) -> dict:
"""Fetch user profile with context-aware logging."""
# Context is available as the ctx parameter
return {"id": user_id}
Prompts
New in version: 2.2.5
from fastmcp import FastMCP, Context
mcp = FastMCP(name="Context Demo")
@mcp.prompt
async def data_analysis_request(dataset: str, ctx: Context) -> str:
"""Generate a request to analyze data with contextual information."""
# Context is available as the ctx parameter
return f"Please analyze the following dataset: {dataset}"
Via Runtime 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:
from fastmcp import FastMCP
from fastmcp.server.dependencies import get_context
mcp = FastMCP(name="Dependency Demo")
# Utility function that needs context but doesn't receive it as a parameter
async def process_data(data: list[float]) -> dict:
# Get the active context - only works when called within a request
ctx = get_context()
await ctx.info(f"Processing {len(data)} data points")
@mcp.tool
async def analyze_dataset(dataset_name: str) -> dict:
# Call utility function that uses context internally
data = load_data(dataset_name)
await process_data(data)
- The
get_context function should only be used within the context of a server request. Calling it outside of a request will raise a RuntimeError.
- 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.
await ctx.debug("Starting analysis")
await ctx.info(f"Processing {len(data)} items")
await ctx.warning("Deprecated parameter used")
await ctx.error("Processing failed")
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.
result = await ctx.elicit("Enter your name:", response_type=str)
if result.action == "accept":
name = result.data
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.
response = await ctx.sample("Analyze this data", temperature=0.7)
Progress Reporting
Update clients on the progress of long-running operations, enabling progress indicators and better user experience.
await ctx.report_progress(progress=50, total=100) # 50% complete
Resource Access
Read data from resources registered with your FastMCP server, allowing access to files, configuration, or dynamic content.
content_list = await ctx.read_resource("resource://config")
content = content_list[0].content
ctx.read_resource(uri: str | AnyUrl) -> list[ReadResourceContents]: Returns a list of resource content parts
State Management
New in version: 2.11.0
Store and share data across middleware and tool calls within a request. Context objects maintain a state dictionary that’s especially useful for passing information from middleware to your tools.
To store a value in the context state, use ctx.set_state(key, value). To retrieve a value, use ctx.get_state(key).
This simplified example shows how to use MCP middleware to store user info in the context state, and how to access that state in a tool:
from fastmcp.server.middleware import Middleware, MiddlewareContext
class UserAuthMiddleware(Middleware):
async def on_call_tool(self, context: MiddlewareContext, call_next):
# Middleware stores user info in context state
context.fastmcp_context.set_state("user_id", "user_123")
context.fastmcp_context.set_state("permissions", ["read", "write"])
return await call_next()
@mcp.tool
async def secure_operation(data: str, ctx: Context) -> str:
"""Tool can access state set by middleware."""
user_id = ctx.get_state("user_id") # "user_123"
permissions = ctx.get_state("permissions") # ["read", "write"]
if "write" not in permissions:
return "Access denied"
return f"Processing {data} for user {user_id}"
ctx.set_state(key: str, value: Any) -> None: Store a value in the context statectx.get_state(key: str) -> Any: Retrieve a value from the context state (returns None if not found)
State Inheritance:
When a new context is created (nested contexts), it inherits a copy of its parent’s state. This ensures that:
- State set on a child context never affects the parent context
- State set on a parent context after the child context is initialized is not propagated to the child context
This makes state management predictable and prevents unexpected side effects between nested operations.
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:
@mcp.tool
async def custom_tool_management(ctx: Context) -> str:
"""Example of manual notification after custom tool changes."""
# After making custom changes to tools
await ctx.send_tool_list_changed()
await ctx.send_resource_list_changed()
await ctx.send_prompt_list_changed()
return "Notifications sent"
FastMCP Server
To access the underlying FastMCP server instance, you can use the ctx.fastmcp property:
@mcp.tool
async def my_tool(ctx: Context) -> None:
# Access the FastMCP server instance
server_name = ctx.fastmcp.name
...
MCP Request
Access metadata about the current request and client.
@mcp.tool
async def request_info(ctx: Context) -> dict:
"""Return information about the current request."""
return {
"request_id": ctx.request_id,
"client_id": ctx.client_id or "Unknown client"
}
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.
Runtime Dependencies
HTTP Requests
New in version: 2.2.11
The recommended way to access the current HTTP request is through the get_http_request() dependency function:
from fastmcp import FastMCP
from fastmcp.server.dependencies import get_http_request
from starlette.requests import Request
mcp = FastMCP(name="HTTP Request Demo")
@mcp.tool
async def user_agent_info() -> dict:
"""Return information about the user agent."""
# Get the HTTP request
request: Request = get_http_request()
# Access request data
user_agent = request.headers.get("user-agent", "Unknown")
client_ip = request.client.host if request.client else "Unknown"
return {
"user_agent": user_agent,
"client_ip": client_ip,
"path": request.url.path,
}
- You need access to HTTP information in helper functions
- You’re calling nested functions that need HTTP request data
- You’re working with middleware or other request processing code
New in version: 2.2.11
If you only need request headers and want to avoid potential errors, you can use the get_http_headers() helper:
from fastmcp import FastMCP
from fastmcp.server.dependencies import get_http_headers
mcp = FastMCP(name="Headers Demo")
@mcp.tool
async def safe_header_info() -> dict:
"""Safely get header information without raising errors."""
# Get headers (returns empty dict if no request context)
headers = get_http_headers()
# Get authorization header
auth_header = headers.get("authorization", "")
is_bearer = auth_header.startswith("Bearer ")
return {
"user_agent": headers.get("user-agent", "Unknown"),
"content_type": headers.get("content-type", "Unknown"),
"has_auth": bool(auth_header),
"auth_type": "Bearer" if is_bearer else "Other" if auth_header else "None",
"headers_count": len(headers)
}
get_http_headers() excludes problematic headers like host and content-length. To include all headers, use get_http_headers(include_all=True).
Access Tokens
New in version: 2.11.0
When using authentication with your FastMCP server, you can access the authenticated user’s access token information using the get_access_token() dependency function:
from fastmcp import FastMCP
from fastmcp.server.dependencies import get_access_token, AccessToken
mcp = FastMCP(name="Auth Token Demo")
@mcp.tool
async def get_user_info() -> dict:
"""Get information about the authenticated user."""
# Get the access token (None if not authenticated)
token: AccessToken | None = get_access_token()
if token is None:
return {"authenticated": False}
return {
"authenticated": True,
"client_id": token.client_id,
"scopes": token.scopes,
"expires_at": token.expires_at,
"token_claims": token.claims, # JWT claims or custom token data
}
- Access user identification - Get the
client_id or subject from token claims
- Check permissions - Verify scopes or custom claims before performing operations
- Multi-tenant applications - Extract tenant information from token claims
- Audit logging - Track which user performed which actions
Working with Token Claims
The claims field contains all the data from the original token (JWT claims for JWT tokens, or custom data for other token types):
from fastmcp import FastMCP
from fastmcp.server.dependencies import get_access_token
mcp = FastMCP(name="Multi-tenant Demo")
@mcp.tool
async def get_tenant_data(resource_id: str) -> dict:
"""Get tenant-specific data using token claims."""
token: AccessToken | None = get_access_token()
# Extract tenant ID from token claims
tenant_id = token.claims.get("tenant_id") if token else None
# Extract user ID from standard JWT subject claim
user_id = token.claims.get("sub") if token else None
# Use tenant and user info to authorize and filter data
if not tenant_id:
raise ValueError("No tenant information in token")
return {
"resource_id": resource_id,
"tenant_id": tenant_id,
"user_id": user_id,
"data": f"Tenant-specific data for {tenant_id}",
}
