HTTP/Web Bad Request

The HTTP 400 Bad Request status code indicates that the server cannot or will not process the request due to something perceived as a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

Common Causes

Malformed request syntax (e.g., invalid JSON or XML in the request body).
Missing required request parameters or headers.
Request entity (body) is too large or in an unsupported format.
Invalid URL encoding or query string parameters.

How to Fix

1 Validate Client-Side Request

Ensure the request being sent from the client (browser, app, script) is correctly formatted. Check the URL, headers, and body payload.

BASH

 $ # Example using curl to test a POST request with correct JSON
curl -X POST https://api.example.com/endpoint \
  -H "Content-Type: application/json" \
  -d '{"key": "value"}'

2 Check Server-Side Logs

Examine the web server or application logs for more specific details about why the request was rejected. The logs often contain the exact validation error.

BASH

 $ # Example for checking Nginx error logs
tail -f /var/log/nginx/error.log

# Example for checking a Node.js/Express app console output

3 Use a Debugging Proxy

Inspect the raw HTTP request and response using a tool like curl with verbose mode or a proxy like Burp Suite/Charles to identify malformed headers or body content.

BASH

 $ curl -v -X POST https://api.example.com/endpoint \
  -H "Content-Type: application/json" \
  -d '{"key": "value"}'