What class of response is HTTP 400?

HTTP 400 is a 4xx Client Error response. These indicate a client-side error.

How do I fix HTTP 400 Bad Request?

HTTP 400 is a client error. Verify the request URL, method, headers, and body are correct. Consult the API documentation for the endpoint.

Is HTTP 400 an error?

Yes, HTTP 400 is an error — specifically a 4xx Client Error code.

HTTP 400 Bad Request: What It Means and When You See It

Quick Answer

HTTP 400 Bad Request means the server cannot process the request due to a client error — malformed syntax, invalid request message framing, or deceptive request routing.

Common Causes of HTTP 400

HTTP 400 Bad Request is returned when the server cannot process the request due to client error. Common causes: malformed JSON in the request body (missing closing bracket, trailing comma), wrong Content-Type header (sending JSON with text/plain), missing required query parameters, invalid URL encoding, request headers that are too large (cookie overflow), and HTTP/2 protocol violations. Check the request body format, headers, and URL structure first.

Fixing HTTP 400 Errors

Validate JSON before sending: JSON.parse(body) in JavaScript, json.loads(body) in Python. Check Content-Type matches the body format: application/json for JSON, multipart/form-data for file uploads. Verify all required fields are present and correctly typed. In curl: curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' URL. If the API returns a 400, read the response body - most APIs include a message or errors field explaining what was wrong.

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Frequently Asked Questions

Related Values

100

HTTP 100 Continue means the server has received the request headers and the client should proceed to send the request body. It is an interim response used to inform the client to continue.

101

HTTP 101 Switching Protocols indicates the server is switching to the protocol specified in the Upgrade header field. Commonly used when upgrading to WebSocket connections.

200

HTTP 200 OK is the standard success response. The request has succeeded and the server has returned the requested resource in the response body.

201

HTTP 201 Created means the request succeeded and a new resource was created as a result. The Location header typically points to the new resource URL.