HTTP status codes

A practical map of common HTTP status codes and when to use them.

2xx success

200 OK: Standard success for GET and many POST handlers.
201 Created: A resource was created; often include a Location header.
204 No Content: Success with an empty body (common for DELETE).

3xx redirects

301 Moved Permanently: Permanent redirect; caches may remember it.
302 Found: Temporary redirect.
304 Not Modified: Client cache is still valid.

4xx client errors

400 Bad Request: Malformed input the server cannot process.
401 Unauthorized: Authentication is missing or invalid.
403 Forbidden: Authenticated but not allowed.
404 Not Found: No matching resource.
409 Conflict: State conflict (duplicate key, version clash).
429 Too Many Requests: Rate limit exceeded.

5xx server errors

500 Internal Server Error: Unhandled server failure.
502 Bad Gateway: Upstream proxy got an invalid response.
503 Service Unavailable: Temporarily down or overloaded.
504 Gateway Timeout: Upstream did not answer in time.

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