Getting 'Error 431: Request Header Fields Too Large' – How Do I Fix This? or What Causes Error 431 an

error 431 is such a mood killer. Happened to me on WordPress sites—turns out some plugins go wild with headers.

If you’re the site owner, check your .htaccess or nginx.conf. For users, try:
- Switching to HTTP/1.1 (some sites hate HTTP/2)
- Using a bookmarklet to strip headers (like "Header Editor" extension)