4xx Client Error

HTTP 431 Request Header Fields Too Large

The server is unwilling to process the request because its header fields are too large. This can happen when cookies, authorization tokens, or other headers are excessively long.

Common Causes

  • Cookies have grown too large (accumulated over time)
  • Authorization token is excessively long
  • Too many custom headers in the request
  • Referrer URL is extremely long

How to Fix

  1. 1Clear browser cookies for the domain and re-authenticate
  2. 2Reduce the size of custom headers
  3. 3Increase server's header size limit if you control it
  4. 4Move large data from headers to the request body

Example

HTTP 431 Request Header Fields Too Large
GET /page HTTP/1.1
Cookie: (extremely long cookie string)

→ 431 Request Header Fields Too Large

Related Client Error Codes

400

Bad Request

401

Unauthorized

402

Payment Required

403

Forbidden

404

Not Found

405

Method Not Allowed

406

Not Acceptable

407

Proxy Authentication Required

408

Request Timeout

409

Conflict

410

Gone

411

Length Required

412

Precondition Failed

413

Content Too Large

414

URI Too Long

415

Unsupported Media Type

416

Range Not Satisfiable

417

Expectation Failed

418

I'm a Teapot

421

Misdirected Request

422

Unprocessable Content

423

Locked

424

Failed Dependency

425

Too Early

426

Upgrade Required

428

Precondition Required

429

Too Many Requests

451

Unavailable For Legal Reasons