400
Bad Request
Client errors (4xx)·RFC 9110
What 400 means
The server cannot process the request due to a client error (malformed syntax, invalid data).
Common causes: malformed JSON, missing required fields, invalid query parameters, or a request that is too large to parse.
Client errors (4xx)
The request contains an error from the client — bad syntax, missing auth or a wrong URL.
Other 4xx codes
401Unauthorized402Payment Required403Forbidden404Not Found405Method Not Allowed406Not Acceptable407Proxy Authentication Required408Request Timeout409Conflict410Gone411Length Required412Precondition Failed413Content Too Large414URI Too Long415Unsupported Media Type416Range Not Satisfiable417Expectation Failed418I'm a teapot421Misdirected Request422Unprocessable Content423Locked424Failed Dependency425Too Early426Upgrade Required428Precondition Required429Too Many Requests431Request Header Fields Too Large451Unavailable For Legal Reasons
FAQ — 400
What does HTTP 400 mean?
400 Bad Request: The server cannot process the request due to a client error (malformed syntax, invalid data). Common causes: malformed JSON, missing required fields, invalid query parameters, or a request that is too large to parse.
Which class does status code 400 belong to?
400 is a Client errors (4xx) code. The request contains an error from the client — bad syntax, missing auth or a wrong URL.
Where is the 400 code defined?
Status code 400 is defined in RFC 9110 and is part of the IANA HTTP Status Code Registry.