HTTP 401 Unauthorized

When is 401 used?

• Missing or invalid API key
• Expired JWT token
• Login required but not provided

How to handle a 401 response

Inspect the request — URL, method, headers, credentials, and body. Retrying the same request unchanged will usually fail again; 429 is the exception, where you should wait for the Retry-After period.

Check the status code a URL returns from the command line:

curl -s -o /dev/null -w "%{http_code}\n" https://example.com

How to return 401 from your server

Node.js (Express)

res.status(401).json({ message: 'Unauthorized' });

Python (Flask)

return {"message": "Unauthorized"}, 401

Go (net/http)

w.WriteHeader(401)