HTTP Status Codes

431 Request Header Fields Too Large

The request's header section is too large for the server to process — frequently caused by a bloated Cookie header or too many custom headers.

What it means

431 Request Header Fields Too Large (RFC 6585) means the total header size, or a single field, exceeds server limits. The usual culprit is an oversized Cookie header. The fix is to shrink cookies and remove unnecessary headers.

Why it matters

  • It protects servers from memory exhaustion via huge header blocks.
  • It points at cookie bloat that also slows every request.

Common mistakes

  • Accumulating large or numerous cookies until requests exceed the header limit.

How WebInspect checks this

  • WebInspect reports cookies and header sizes so header bloat is visible.