CORS & Custom Middleware in Python

From the FastAPI cheat sheet · Middleware & CORS · verified Jul 2026

CORS & Custom Middleware

Configure CORS and write custom middleware for logging, timing, etc.

python

from fastapi.middleware.cors import CORSMiddleware

app.add_middleware(
    CORSMiddleware,
    allow_origins=["http://localhost:3000"],
    allow_methods=["*"],
    allow_headers=["*"],
    allow_credentials=True,
)

💡 Middleware runs on every request/response — use for logging, timing, auth checks

⚡ Set allow_origins to specific domains in production — never use ["*"] with credentials

📌 Middleware order matters — they execute in reverse order of how they're added

🟢 Built-in middleware: CORSMiddleware, TrustedHostMiddleware, HTTPSRedirectMiddleware

corsmiddleware

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