HTTP 400 Bad Request
Client Error4xx Response — Bad Request
What Does HTTP 400 Mean?
HTTP 400 Bad Request indicates that the server cannot process the request due to a client error. The request is malformed, contains invalid syntax, deceptive routing, or is otherwise incorrect.
The server sends 400 when it cannot understand what the client is asking for. This differs from 404 (resource not found) and 403 (access denied). A 400 means the request itself is fundamentally wrong.
Common scenarios include: invalid JSON in the request body, missing required parameters, malformed URLs, invalid header values, exceeding URL length limits, and invalid request framing. The response body should include details about what was wrong with the request.
Common Causes of 400 Bad Request
The server cannot parse or understand the request. Common causes: malformed JSON/XML in the request body, missing required parameters, invalid query string syntax, corrupted request headers, and invalid URL encoding.
Additional causes include: request body too large (without a specific 413 response), invalid date formats, unsupported parameter values, and conflicting request parameters.
How to Fix 400 Bad Request
For developers: validate all input data before processing, return descriptive error messages in the response body, and log the malformed request for debugging. For API users: check your request format against the API documentation, validate JSON syntax, and ensure all required parameters are included.
Use tools like Postman or curl to test your requests and compare with the API documentation.
Related Status Codes
Frequently Asked Questions
What does HTTP 400 mean?
HTTP 400 Bad Request is a client error response. HTTP 400 Bad Request indicates that the server cannot process the request due to a client error. The request is malformed, contains invalid syntax, deceptive routing, or is otherwise incorrect.
Is HTTP 400 an error?
Yes, HTTP 400 is a client error. Client Error responses (cli) indicate the request contains an error.
How do I fix HTTP 400?
For developers: validate all input data before processing, return descriptive error messages in the response body, and log the malformed request for debugging. For API users: check your request format against the API documentation, validate JSON synt
What causes HTTP 400 Bad Request?
The server cannot parse or understand the request. Common causes: malformed JSON/XML in the request body, missing required parameters, invalid query string syntax, corrupted request headers, and invalid URL encoding.
Is HTTP 400 permanent or temporary?
HTTP 400 is situational — it depends on the underlying cause. Fix the root cause to resolve it.
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