HTTP Status Codes

The request headers are OK; client should send the body.

Server is switching protocols (e.g. to WebSocket).

Standard success response.

Resource was created. Include a Location header.

Request accepted but not yet processed.

Success with no body — common after PUT/DELETE.

Range request was honoured.

Permanent redirect — search engines update the index.

Temporary redirect — keep the original URL.

Used after POST to redirect to a GET resource.

Cached version is still valid; reuse it.

Like 302 but the method must not change.

Like 301 but the method must not change.

Malformed request — fix the client.

Authentication is required or has failed.

Reserved for future use; some APIs use it for paid tiers.

Authenticated but not allowed.

Resource does not exist.

Endpoint exists but doesn't accept this verb.

Server can't produce a response matching Accept headers.

Client took too long to send the request.

Request conflicts with current resource state (e.g. duplicate).

Resource is permanently removed — stronger than 404.

Content-Length header is missing.

If-Match / If-None-Match condition failed.

Request body exceeds server limit.

URL exceeds server limit.

Server doesn't accept the request's Content-Type.

An April Fools' joke from 1998 — kept alive ever since.

Validation failed — request was syntactically OK.

Reject replays of early data.

Server requires conditional headers.

Rate limit exceeded — back off.

Headers exceed server limit.

Blocked due to a legal demand.

Generic server crash — check logs.

Server doesn't support this functionality.

Upstream server returned an invalid response.

Server is overloaded or down for maintenance.

Upstream server didn't respond in time.

Server doesn't support the HTTP version.

Server is out of disk space.

Server detected an infinite loop while processing.

Captive portal — log in to the network first.