431 Request Header Fields Too Large

What 431 Request Header Fields Too Large means {#what}

The server won’t process the request because the total header size (or a single header) exceeds its limits. Often triggered by bloated cookies.

When you’ll see a 431 {#when}

• Cookie accumulation making headers enormous
• Very long Authorization tokens
• Too many custom headers

When to use 431 {#use}

• Include whether the issue is the total size or a specific header
• Common fix on the client side: clear cookies or reduce header payload