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4xx Client & Proxy Request

HTTP 431 Request Header Fields Too Large — Reverse Proxy & Gateway Troubleshooting

HTTP 431 Request Header Fields Too Large rejects requests when either an individual HTTP header field or the cumulative header block exceeds server memory limits.

Status Code431 Request Header Fields Too Large
Specification / OriginRFC 6585 §5
Failure LayerHTTP/1.1 & HTTP/2 HPACK Parser
Retry SafetyDo not blind-retry without fixing request syntax, auth, or origin certificate

Interactive HTTP 431 Live Probe & Log Command Builder

Enter your target endpoint below to generate copy-ready curl latency breakdown probes and origin bypass tests:


  

    Related diagnostics:
    Nginx & Caddy Proxy Generator → ·
    X.509 SSL Certificate Decoder → ·
    Offline JWT Expiry Inspector →
  






  
Production Root Causes & Remediation Guide

  
Node.js (--max-http-header-size, historically 8 KiB or 16 KiB), Envoy, and Go HTTP servers return 431 when enterprise SAML/OIDC claims pack dozens of RBAC group UUIDs into a JWT cookie, or when stale tracking cookies accumulate on a root domain.

  
Step-by-Step Engineering Fix

  
Trim bloated JWT claims down to compact user IDs, scope authentication cookies to dedicated auth. subdomains so static asset requests stay tiny, or pass --max-http-header-size=32768 to Node.js.

  
Recommended Nginx / Reverse-Proxy Configuration Snippet

  
# Launch Node.js upstream with 32 KiB max header allowance
NODE_OPTIONS="--max-http-header-size=32768" node server.js







  
Frequently Asked Questions (HTTP 431)

  
  

    How do you fix HTTP 431 on localhost or subdomain web apps?
    
Clear accumulated domain cookies for localhost/root domains and move verbose RBAC permission arrays out of client cookies into server-side or compact token lookups.

  

  
  

    Which infrastructure layer generates HTTP 431 Request Header Fields Too Large?
    
HTTP 431 (RFC 6585 §5) typically originates at the HTTP/1.1 & HTTP/2 HPACK Parser layer. HTTP 431 Request Header Fields Too Large rejects requests when either an individual HTTP header field or the cumulative header block exceeds server memory limits.

  

  
  

    Should API clients automatically retry HTTP 431 responses?
    
Do not blind-retry HTTP 431 without fixing the underlying request payload, authentication token, or origin TLS certificate first.

  

  






  
Browse All 25 Gateway, Proxy & Cloud HTTP Error Guides

  

    
      HTTP 400 (Bad Request)
    
      HTTP 401 (Unauthorized)
    
      HTTP 403 (Forbidden)
    
      HTTP 404 (Not Found)
    
      HTTP 405 (Method Not Allowed)
    
      HTTP 408 (Request Timeout)
    
      HTTP 413 (Content Too Large)
    
      HTTP 422 (Unprocessable Content)
    
      HTTP 429 (Too Many Requests)
    
      HTTP 431 (Request Header Fields Too Large)
    
      HTTP 499 (Client Closed Request)
    
      HTTP 500 (Internal Server Error)
    
      HTTP 501 (Not Implemented)
    
      HTTP 502 (Bad Gateway)
    
      HTTP 503 (Service Unavailable)
    
      HTTP 504 (Gateway Timeout)
    
      HTTP 507 (Insufficient Storage)
    
      HTTP 511 (Network Authentication Required)
    
      HTTP 520 (Web Server Returned an Unknown Error)
    
      HTTP 521 (Web Server Is Down)
    
      HTTP 522 (Connection Timed Out)
    
      HTTP 523 (Origin Is Unreachable)
    
      HTTP 524 (A Timeout Occurred)
    
      HTTP 525 (SSL Handshake Failed)
    
      HTTP 526 (Invalid SSL Certificate)
    
  






  


  
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