Request Header Fields Too Large
4xx Client Error
Last updated:
The server is unwilling to process the request because header fields are too large.
Description
Usually caused by oversized cookies or Authorization headers. Fixing this requires reducing cookie size on the client, not on the server.
When to use
Return 431 for pathological header sizes. Most servers have built-in limits (nginx: 8k, Apache: 8k default).
Specification
RFC 6585
Examples
HTTP response
HTTP/1.1 431 Request Header Fields Too Large
Content-Type: application/json
{"error":"Request Header Fields Too Large"}Node.js (Express)
res.status(431).json({ error: "Request Header Fields Too Large" });Go (net/http)
w.WriteHeader(http.Status431)
Python (Flask)
return jsonify({"error": "Request Header Fields Too Large"}), 431Related status codes
All 4xx codes
400 Bad Request401 Unauthorized403 Forbidden404 Not Found405 Method Not Allowed406 Not Acceptable408 Request Timeout409 Conflict410 Gone411 Length Required412 Precondition Failed413 Payload Too Large414 URI Too Long415 Unsupported Media Type418 I'm a teapot422 Unprocessable Entity425 Too Early428 Precondition Required429 Too Many Requests431 Request Header Fields Too Large451 Unavailable For Legal Reasons