The “431 Request Header Fields too Large” is an HTTP client error status code 431 that occurs when a server terminates a request because the HTTP headers are excessively long. This 431 status code indicates that either the total size of all request headers combined is too large, or a single header field exceeds the server’s size limit.
When you face “request failed with status code 431”, it means your browser’s request contains too much header information for the server to handle, but you can typically resolve this by reducing the header size.
What Causes the 431 Request Header Fields too Large?
Several factors can trigger a “431 request header fields too large react” error. The most common cause is an excessive number of cookies stored in your browser for a particular website. When you visit any site, your browser sends all related cookies in the request headers, and if there are too many, it can exceed the server’s limit.
Another common trigger is extremely long referrer URLs, especially in single-page applications built with React or similar frameworks.
Example
Request:
GET /api/data HTTP/1.1
Host: example.com
Cookie: session=abc123; user_pref=xyz789; analytics=def456; tracking=ghi789;
custom=jkl012; theme=mno345; language=pqr678; region=stu901;
[... hundreds more cookies ...]
Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
Referer: https://example.com/very/long/path/with/many/parameters?id=123&type=user...
Response:
HTTP/1.1 431 Request Header Fields Too Large
Content-Type: application/json
{
"error": "431 Request Header Fields Too Large",
"message": "The total size of request headers exceeds server limit. Please clear your cookies and try again.",
"status": 431
}
In this example, the combination of numerous cookies, a long authorization token, and an extensive referrer URL causes the total header size to exceed the server’s limits, triggering the 431 error response.
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