400
Bad Request
The server cannot process the request because of a client-side error. The request has malformed syntax, invalid parameters, or is otherwise unreadable by the server.
What does HTTP 400 mean?
The server cannot process the request because of a client-side error. The request has malformed syntax, invalid parameters, or is otherwise unreadable by the server.
Common causes
- 1
Malformed JSON or XML in the request body — missing commas, unclosed brackets, or invalid encoding.
- 2
Invalid or missing required query parameters, headers, or form fields that the server expects.
- 3
URL contains invalid characters, is too long, or has a malformed query string.
How to fix it
- 1
Inspect the request in browser dev tools (Network tab). Check the request body, headers, and URL for formatting errors.
- 2
Validate your JSON payload with a linter before sending. Ensure Content-Type matches the body format (application/json for JSON, etc.).
- 3
Read the response body — most APIs include a detailed error message explaining which field or parameter is invalid.
Monitor for HTTP 400 errors
If your endpoint starts returning 400 errors to valid requests, it often means a deployment broke input parsing. Uptrack detects the status code change and alerts you before users file bug reports.
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