# 501 Not Implemented

> The server does not support the functionality required to fulfill the request.

Source: https://apiguide.dev/status-codes/501
Class: server-error
Defined in: RFC 9110, Section 15.6.2 <https://www.rfc-editor.org/rfc/rfc9110.html#section-15.6.2>
Updated: 2026-07-09

## What does HTTP status code 501 mean?

The 501 Not Implemented status code indicates that the server does not support or recognize the request method or capability.

## When to use it in APIs

Used when stubbing out new endpoints or when an API does not support certain standard HTTP operations (like a read-only API receiving a DELETE request).

## How it compares to other codes

* **405 Method Not Allowed**: Implies the method *is* recognized by the server but is not permitted on that specific route. 501 implies the server lacks the capacity to perform the method globally.