Request Header Fields Too Large
Production Risk
Low. It's a protective measure for the server. The error is rare and almost always points to a bug in the client or web application creating excessively large headers.
The server is unwilling to process the request because its header fields are too large. The request may be resubmitted after reducing the size of the request header fields.
- 1A client is sending a very large number of cookies.
- 2A client is sending an exceptionally long 'Authorization' header or other custom headers.
- 3The total size of all headers combined exceeds the server's configured limit.
A website sets too many cookies, and on subsequent requests, the size of the 'Cookie' header exceeds the server's limit (e.g., 8KB).
GET / HTTP/1.1 Host: example.com Cookie: ... (imagine many kilobytes of cookie data)
expected output
HTTP/1.1 431 Request Header Fields Too Large
Fix 1
Reduce Header Size
WHEN You control the client or server setting the headers (like cookies).
Consolidate cookies, use session storage instead of cookies for non-essential data, or shorten other header values.
Why this works
Application Logic
Fix 2
Increase Server's Header Limit
WHEN You control the server and the large headers are necessary.
// Nginx example in nginx.conf large_client_header_buffers 4 16k;
Why this works
Server Configuration
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