HTTP Requests

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Overview

When running FastMCP as a web server, your MCP tools, resources, and prompts might need to access the underlying HTTP request information, such as headers, client IP, or query parameters.

FastMCP provides a clean way to access HTTP request information through a dependency function.

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Accessing HTTP Requests

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,
    }

This approach works anywhere within a request’s execution flow, not just within your MCP function. It’s useful when:

1. You need access to HTTP information in helper functions
2. You’re calling nested functions that need HTTP request data
3. You’re working with middleware or other request processing code

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Accessing HTTP Headers Only

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)
    }

By default, get_http_headers() excludes problematic headers like host and content-length. To include all headers, use get_http_headers(include_all=True).

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Important Notes

• HTTP requests are only available when FastMCP is running as part of a web application
• Accessing the HTTP request with get_http_request() outside of a web request context will raise a RuntimeError
• The get_http_headers() function never raises errors - it returns an empty dict when no request context is available
• The get_http_request() function returns a standard Starlette Request object