HTTP Status Code Reference (1xx-5xx)

Server received headers, client may proceed sending the body.

Server agrees to switch protocols (e.g. HTTP → WebSocket).

Early hints (preload, preconnect) before the final response.

Success. Standard response for GET.

Resource was created (POST/PUT). Location header points to the new resource.

Request accepted but not yet processed (async job).

Success but no body. Common for DELETE.

Partial resource — used for range requests (video streaming, resume download).

Resource permanently moved to a new URL. SEO-friendly — Google updates the index.

Temporary redirect. Unlike 301, Google does not update the canonical.

After a POST, GET the resource at the Location URL (PRG pattern).

Cache is still valid, no body sent — saves bandwidth.

Like 302 but preserves the method (POST stays POST).

Like 301 but preserves the method.

Malformed request (bad JSON, missing field…).

Not authenticated — retry with valid credentials.

Authenticated but lacks permission — do not confuse with 401.

Resource not found. Bad URL or deleted.

URL exists but the method is not allowed (e.g. POST to a GET-only endpoint).

Server waited too long for the client to finish the request.

State conflict — e.g. editing the same record with stale version.

Resource permanently deleted — Google removes from the index.

Request body exceeds server limit.

Content-Type not supported — e.g. sending XML to a JSON-only endpoint.

RFC 2324 joke (1998). The server cannot brew coffee because it is a teapot.

Syntax OK but validation failed (bad email format, negative number…).

Rate limit hit. Retry-After header indicates when to retry.

Generic server error — check server logs.

Server does not implement this method.

Server acting as proxy got a bad response from upstream.

Server temporarily down/overloaded. Retry-After indicates when to come back.

Gateway did not receive a response from upstream in time.

Network auth required (e.g. hotel WiFi captive portal).