Introduction
Many website owners and users suddenly face an error message that says “Request header too large” while opening a website or submitting a form. This error is confusing because it appears without any warning and often works fine after clearing browser data or trying again later.
In simple words, this error occurs when the information sent by the browser to the server becomes bigger than what the server is willing to accept. This information is called the request header, and it usually contains cookies, authentication tokens, and other metadata. When the header size crosses the server limit, the request is rejected.
This article explains why this error happens and how to fix it in a clear, practical, and easy-to-understand way.
What Is a Request Header?
Every time a browser communicates with a web server, it sends some basic information along with the request. This information includes cookies, session IDs, authorization data, browser details, and language preferences.
Think of a request header like an envelope attached to a letter. If the envelope becomes too thick because too many documents are stuffed inside, the post office refuses to deliver it. The same logic applies to web servers.
Too Many Cookies Stored in the Browser
One of the most common reasons for this error is too many cookies stored for a website. Each cookie adds extra data to the request header.
For example, a website may store multiple tracking cookies, session cookies, and user preference cookies. Over time, these cookies accumulate and increase header size.
When the browser sends all these cookies together, the server rejects the request because the header becomes too large.
Large Authentication Tokens or Session Data
Modern web applications often use tokens for authentication. These tokens are stored in cookies or headers.
If tokens become very large or are duplicated multiple times, the request header grows quickly. This commonly happens in single-page applications or systems with complex authentication logic.
Users may experience this issue after logging in and out multiple times or switching between accounts.
Misconfigured Reverse Proxy or Load Balancer
Many websites use reverse proxies or load balancers in front of the main server. These components also have header size limits.
If the proxy limit is smaller than the application server limit, requests may fail even though the backend server can handle them.
This issue often appears after infrastructure changes or cloud migrations.
Repeated Redirects Increasing Header Size
Sometimes, a website enters a redirect loop where cookies or headers are added repeatedly during redirection.
For example, a login page may redirect between authentication and home pages, adding new cookies each time. Eventually, the header becomes too large.
This problem may affect some users but not others, making it harder to detect.
Browser Cache and Corrupted Cookies
Corrupted or outdated cookies can also cause this error. Even a small cookie issue can break the request structure.
Users often notice that opening the website in incognito mode works fine. This is a strong sign that the issue is related to browser-stored data rather than the server itself.
How to Fix: Clear Browser Cookies and Cache
The simplest fix for users is to clear cookies and cache for the affected website.
This removes unnecessary or corrupted cookies and reduces the request header size. After clearing data, the website usually starts working normally.
This is why support teams often suggest clearing browser data as a first step.
How to Fix: Reduce Cookie Usage in the Application
From a developer perspective, unnecessary cookies should be removed. Only essential cookies should be stored and sent with every request.
Avoid storing large data in cookies. Instead, keep minimal identifiers and store actual data on the server.
This approach improves performance and reduces the chance of header size errors.
How to Fix: Increase Header Size Limits on Server
Web servers allow configuration of maximum request header size. If the application genuinely needs larger headers, server limits can be adjusted carefully.
This should be done cautiously, as increasing limits too much can impact security and performance.
It is best to balance application needs with server safety.
How to Fix: Review Proxy and Load Balancer Settings
If a reverse proxy or load balancer is used, its header size limits must match or exceed backend server limits.
Mismatch in these configurations is a common cause of this error in production environments.
Regular configuration reviews help avoid such issues.
How to Fix: Prevent Redirect Loops
Redirect logic should be reviewed to ensure cookies are not repeatedly added during redirects.
Fixing redirect loops not only resolves header size errors but also improves user experience and SEO performance.
Summary
The “Request header too large” error occurs when the browser sends more header data than the server allows, usually due to too many cookies, large authentication tokens, redirect loops, or misconfigured proxies. While users can often fix the issue by clearing browser cookies, long-term solutions involve reducing cookie usage, optimizing authentication logic, fixing redirects, and properly configuring server and proxy limits. Understanding and addressing these causes helps ensure stable, secure, and smooth communication between browsers and web servers.