HTTP 400 Bad Request — What It Means and How to Fix It

Common Causes

• Malformed request syntax (e.g., invalid HTTP headers, incorrect method)
• Invalid or missing required parameters in the request body or query string
• Request body too large or exceeding server limits
• Invalid characters in URLs or headers
• Security violations (e.g., attempting to inject malicious code)

Code Examples to Handle HTTP 400

curl -I https://httpbin.org/status/400

fetch('https://httpbin.org/status/400')
  .then(response => {
    if (response.status === 400) {
      console.log('Handled Bad Request');
    }
  });

import requests

response = requests.get('https://httpbin.org/status/400')
if response.status_code == 400:
    print("Received Bad Request")

How to Fix It

1. Review the request's syntax: Check HTTP headers, method, URL, and body for any malformations or incorrect formatting.
2. Validate request parameters: Ensure all required parameters are present and that their values conform to expected data types and constraints.
3. Check server logs: Server-side logs often provide more specific details about why the request was deemed 'bad'.
4. Reduce request size: If the request body is very large, try sending a smaller request or breaking it into multiple requests.

Related Status Codes