400 Bad Request
A 400 Bad Request error means the server cannot process the request because the client sent something invalid or malformed. This could be due to corrupted syntax, invalid request framing, or deceptive routing. For developers, it typically indicates a problem with how the request was constructed, such as missing required fields, malformed JSON, or invalid query parameters.
Common causes
- Malformed JSON or XML in the request body that the server cannot parse
- Missing required request parameters, headers, or form fields
- URL contains invalid characters, is too long, or has malformed query string encoding
- Request body exceeds the maximum allowed size configured on the server
- Invalid or corrupted cookies being sent with the request
How to fix it
- Validate the request body format using a JSON or XML linter before sending
- Check that all required parameters and headers are included and correctly spelled
- Encode special characters in URLs and query parameters properly using percent-encoding
- Clear browser cookies and cache, then retry the request
- Inspect the raw request with browser DevTools or a tool like curl to identify malformed data
Detect 400 Bad Request errors with Checkend
Checkend monitors your application and alerts you when 400 errors occur, with full request context:
- Full request details (URL, headers, params)
- Server-side stack trace and error context
- Automatic grouping of similar errors
- Instant notifications when error rates spike
Related HTTP errors
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A 422 Unprocessable Entity error means the server understands the request format and syntax, but can...
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