HTTP Status Code Reference

Server received the request headers and the client should send the body.

Causes & fix: Sent in response to an Expect: 100-continue header before a large upload.

Server is switching protocols as requested by the Upgrade header.

Causes & fix: WebSocket handshakes and HTTP/2 upgrades.

The request succeeded.

Causes & fix: Standard success for GET, PUT, POST without resource creation.

The request succeeded and a new resource was created.

Causes & fix: Returned by POST/PUT that create a resource; check the Location header.

The request was accepted for processing but is not complete.

Causes & fix: Async/queued work. Poll a status endpoint for the result.

Success with no response body.

Causes & fix: DELETE operations and PUTs that intentionally return nothing.

The resource has a new permanent URL.

Causes & fix: Domain or path migrations, http to https redirects. Update bookmarks and clients.

The resource is temporarily at a different URL.

Causes & fix: Post-login redirects, A/B routing. Clients should keep using the original URL.

The cached copy is still valid; no body is sent.

Causes & fix: Conditional GET with If-None-Match or If-Modified-Since matched the cache.

Temporary redirect that preserves the request method and body.

Causes & fix: Like 302 but guarantees POST stays POST.

Permanent redirect that preserves the method and body.

Causes & fix: Like 301 but keeps POST as POST. Used for HSTS-style upgrades.

The server cannot process the request due to a client error.

Causes & fix: Malformed JSON, missing required fields, invalid query params. Validate the payload.

Authentication is required or has failed.

Causes & fix: Missing/expired token or bad credentials. Check Authorization header and token expiry.

Authenticated but not allowed to access the resource.

Causes & fix: Insufficient permissions, IP allowlists, WAF rules. Check roles and scopes.

The resource does not exist.

Causes & fix: Wrong path, deleted resource, or routing misconfig. Verify the URL and route table.

The HTTP method is not supported for this resource.

Causes & fix: POST to a GET-only endpoint. Check the Allow header for supported methods.

The server timed out waiting for the request.

Causes & fix: Slow or stalled client uploads, idle keep-alive connections.

The request conflicts with the current state of the resource.

Causes & fix: Duplicate creation, version/ETag mismatch, concurrent edits.

The resource was permanently removed and will not return.

Causes & fix: Deprecated endpoints, purged content. Unlike 404, this is intentional and final.

The server refuses to brew coffee because it is a teapot.

Causes & fix: An April Fools' joke (RFC 2324). Sometimes used as a playful health/easter-egg route.

Syntax is valid but the request is semantically wrong.

Causes & fix: Validation failures on well-formed JSON. Inspect the error body for field details.

The client sent too many requests in a given time.

Causes & fix: Rate limiting. Honor the Retry-After header and add backoff.

A generic, unexpected server-side error.

Causes & fix: Unhandled exceptions, bad deploys. Check application logs and recent releases.

The server does not support the requested functionality.

Causes & fix: Unimplemented method or feature behind a proxy.

A gateway received an invalid response from upstream.

Causes & fix: Upstream app crashed or returned garbage. Check the backend and its health checks.

The server is temporarily unable to handle the request.

Causes & fix: Overload, maintenance, no healthy upstreams. Check autoscaling and Retry-After.

A gateway did not get a timely response from upstream.

Causes & fix: Slow backend, DB locks, downstream timeouts. Check upstream latency and timeouts.

The HTTP version in the request is not supported.

Causes & fix: Misconfigured client or proxy speaking an unsupported protocol version.