The HTTP 400 Bad Request client error response status code indicates that the server would not process the request due to something the server considered to be a client error. The reason for a 400 response is typically due to malformed request syntax, invalid request message framing, or deceptive request routing.

Clients that receive a 400 response should expect that repeating the request without modification will fail with the same error.

Status

400 Bad Request

Examples

Malformed request syntax

Assuming a REST API exists with an endpoint to manage users at http://example.com/users and a POST request with the following body attempts to create a user, but uses invalid JSON with unescaped line breaks:

POST /users HTTP/1.1
Host: example.com
Content-Type: application/json
Content-Length: 38

{
  "email": "b@example.com
",
  "username": "b.smith"
}

If the content is in a valid format, we would expect a 201 Created response or another success message, but instead the server responds with a 400 and the response body includes a message field with some context so the client can retry the action with a properly-formed request:

HTTP/1.1 400 Bad Request
Content-Type: application/json
Content-Length: 71

{
  "error": "Bad request",
  "message": "Request body could not be read properly.",
}

Specifications

See also

• HTTP response status codes
• HTTP Status Code Definitions