# Nginx: 400 Bad Request — Request Header Or Cookie Too Large / client sent too long header line

**Code:** `414 Request-URI Too Large / 400 Request Header Or Cookie Too Large` · **Category:** Nginx / Apache · **Seen on:** Nginx, Linux

The request line or headers (often cookies) exceed `large_client_header_buffers`.

## Meaning

Raise `large_client_header_buffers 4 16k;` (and `client_header_buffer_size 4k`), and reduce cookie bloat: remove old cookies, shorten session data. Typical after apps set many/huge cookies (analytics, auth tokens). Also affects very long query strings (414).

## Common causes

- Large or many cookies
- Very long URLs (414)
- Big JWTs in headers
- Default 8k header buffer
- Cookies accumulating on a shared parent domain

## Quick fix

1. `large_client_header_buffers 4 16k;` in `http`/`server`
2. Clear/shrink cookies; store less in cookies
3. Use POST for large payloads instead of query strings

## Detailed fix by platform

### Nginx

1. `http { client_header_buffer_size 4k; large_client_header_buffers 4 16k; }`

## How to diagnose

1. **Header** — Cookie size?
2. **URL** — Too long?
3. **Buffers** — Value?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/nginx-apache/nginx-large-client-header-buffers)