// http 4xx · client error
HTTP 400 Bad Request
The server can't process a malformed request.
What HTTP 400 Bad Request means
400 Bad Request means the server couldn't understand the request because it's malformed — bad JSON, an invalid parameter, or a broken header. It's a catch-all client error: the request has to change before it can succeed.
Which category is it?
400 is a 4xx code — Client error. 4xx means the request has a problem the client must fix — bad syntax, missing authentication, or a resource that isn't there. It's the caller's responsibility.
Common causes
- Malformed JSON or invalid request body
- Missing or invalid query parameters
- A header the server can't parse
- Request size or syntax limits exceeded
How to fix it
- Validate the request body against the API's schema
- Check required parameters and their types
- Inspect the raw request with a tool like the cURL formatter