Articles/HTTP

HTTP 501 Not Implemented — What It Means

What HTTP status code 501 Not Implemented means, when servers return it, and how to handle it correctly.

Published September 26, 2026

HTTP 501 Not Implemented — The server doesn't support the functionality required to fulfill the request.

Key points

  • Means the server doesn't recognize the request method, or lacks the capability to handle it at all
  • Distinct from 405, which means the method is understood but not allowed on that specific resource
  • Commonly seen when calling an API endpoint documented but not yet implemented
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