What does HTTP status 400 (Bad Request) mean?

 
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HTTP_STATUS_PERMANENT_REDIRECT HTTP_STATUS_DENIED

HTTP_STATUS_BAD_REQUEST

Typical causes include malformed syntax, invalid message framing, inconsistent headers, or deceptive routing information. The status does not identify which field was wrong unless the response body or logs provide details.

Compare the raw request with the endpoint contract: method, URL encoding, host, content type, framing, and body schema. Do not retry unchanged requests automatically.

Typical causes include malformed request syntax, invalid framing, an unusable request target, or other protocol-level defects that prevent normal processing. The response is not a precise application validation code by itself. Capture the actual request line, headers, and body framing before changing higher-level business data.

RFC 9110: HTTP Semantics


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