431
431 Request Header Fields Too Large Error
What This Error Means
The 431 Request Header Fields Too Large error indicates that the server is unwilling to process the request because its header fields are too large. The request may be resubmitted after reducing the size of the request header fields.
Common Causes
- Too many cookies or very large cookies being sent.
- Extremely long Referer URLs.
- Authentication tokens (like JWTs) that are too large.
- Looping redirects accumulating headers.
How to Fix It (For Users)
- 1 Clear your cookies for the site.
- 2 Try accessing the site in Incognito mode.
- 3 Update your browser.
For Site Owners / Developers
- Increase the header size limit in your web server configuration (e.g., `large_client_header_buffers` in Nginx).
- Audit your application's cookie usage and reduce size.
- Check for infinite redirect loops.
When It Is NOT Your Fault
If the website sets an excessive number of cookies.
Check if this outage affects everyone globally
This error often indicates a wider problem. Use our tool to verify if the site is down for everyone.
Check Website Status →Recommended Tool to Prevent This Error
Prevent server timeouts and resource exhaustion with scalable cloud infrastructure.