How To Fix 400 Bad Request: Request Header Or Cookie Too Large

Facing a 400 Bad Request error can be a stumbling block, especially when it specifies the message, “Request Header or Cookie Too Large”. This error surfaces when the data your browser sends exceeds what the Web Hosting server can accept, typically oversized HTTP headers or cookies.

This guide covers why this error occurs and how to fix it. We’ll go through some simple steps to clear out old data from your browser and tweak a few settings to prevent this from happening again.

KEY TAKEAWAYS

• The 400 Bad Request – Request Header or Cookie Too Large error happens when your browser sends more data than the server allows.
• Try using Incognito Mode to check if the problem is related to stored cookies or extensions.
• Clear browser cookies and cache to fix the issue, as this removes unnecessary stored data.
• Some browser extensions can interfere with website requests, so disabling or removing unnecessary ones may help.
• Flush your DNS cache to force your device to refresh outdated network data, which can fix connection issues.
• Restarting your router and modem can also help by clearing temporary network issues that may be causing the error.
• Resolve invalid URLs and compress files to reduce their size before uploading them.
• To prevent this error in the future, keep your browser updated and regularly clear your cookies and cache.

What Does Request Header or Cookie Too Large Error Mean?

This error occurs when your browser sends too much data in the headers or cookies to a server, exceeding its processing limit. This is where a 400 error appears, indicating that “Request Header or Cookie Too Large”.

This can be caused by overly large cookies storing excessive data or bloated HTTP headers filled with too much information. When the server cannot handle the data size received, it rejects the request and displays a 400 error.

The request header too large error is part of the HTTP 4XX status codes, which indicate client-side issues. This error may vary depending on the situation. For example, typing an incorrect web address may result in the Bad Request – It is not a valid request! error message:

Additionally, it may also differ depending on the browser you’re using. Below are some of the error variations:

• HTTP Error 400 – Bad Request
• HTTP Error 400
• HTTP Status 400 – Bad Request
• HTTP Error 400. The request hostname is invalid
• 400 Bad Request. Request Header or Cookie Too Large
• 400 Bad Request
• 400 Bad Request Cookie Too Large
• Bad Request – Your browser sent a request that this server could not understand
• Bad Request – Error 400
• Bad Request – Invalid URL
• 400 – Bad Request. The server could not understand the request due to malformed syntax. The client should not repeat the request without modifications.

Remember, the error message is often vague, lacking specific details about what causes the issue, making it difficult to diagnose and resolve. This highlights the importance of knowing the possible reasons for the request header or cookie too large error.

There are multiple potential reasons:

• Browser Issues: Corrupted cache files, old cookies, or incompatible browser extensions can interfere with your request for the server to process correctly.
• Excessive File Sizes: If your HTTP request includes too many cached images, large cookies, or uploaded files that surpass the server’s capacity, this can lead to an error.
• URL Syntax Errors: Mistakes in the web address, such as typos or incorrect characters, can trigger the 400 error. Something as minor as an extra space or missing symbols, like =, may be the culprit.
• Outdated DNS Cache: If the WordPress site you’re attempting to reach has updated its DNS settings, your old cached data may no longer be valid. This prevents the server from finding the correct IP address.

Now that you know what the 400 error means, why it occurs, and how it can appear, let’s see how to fix it.

6 Ways to Fix 400 Bad Request: Request Header or Cookie Too Large Error

In this section, we show you how to resolve the 400 Bad Request error using the following solutions:

Check Your Internet Connection

An unstable or slow internet connection can sometimes cause a 400 Bad Request error. This happens when your browser tries to send a request, but the data gets cut off or corrupted due to poor connectivity. When this happens, the server cannot understand the request and thus rejects it. 

To see if your internet is the issue, you can run a speed test using tools like: 

• Google Fiber Speed Test
• Ookla Speedtest

When running the test, pay attention to these numbers: 

Download Speed: The speed at which you receive data from the internet. A slow download speed can cause websites to load incorrectly. 

Upload Speed: It shows the speed at which your device sends data. A low upload speed can affect forms, uploads, or any request you send to a website. 

Ping (Latency): A high ping means there is a delay in communication between your device and the server, which can cause errors. 

If your internet connection is weak or slow, there are several steps to try. First, consider restarting your router or modem; this can refresh your connection and increase speed.

If that doesn’t help, switch to a different network. Connecting to another Wi-Fi or using mobile data can help determine if the problem is specific to the initial network. Additionally, for enhanced stability, especially if you’re currently on Wi-Fi, changing to a wired Ethernet connection may assist connection quality.

However, if your internet speed is good and stable, the request header or cookie too large error is not caused by a connection issue. In that case, move on to the next step – checking for typos or invalid characters in the URL.

Fix Invalid URL

Sometimes, a simple mistake in the website address can also trigger this error. The server expects a correctly formatted URL; it can be small, but a typo can prevent it from understanding your request.

For example, consider the URL:

https://www.mysite.com/search?q=hello world

This URL incorrectly includes a space between hello and world. The correct format should replace the space with %20, making it:

https://www.mysite.com/search?q=hello%20world

URL encoding handles these special characters by converting spaces to %20, colons (:) to %3A, and slashes (/) to %2F. If your URL includes characters that haven’t been encoded correctly, the server may be unable to interpret your request, resulting in a 400 error.

Fix URL encoding issues by using an online URL encoder/decoder tool. First, copy your problematic URL and paste it into the tool. Then, click Decode to identify any problematic characters. If necessary, re-encode the URL to correct these formatting errors. After making the adjustments, try reloading the corrected URL in your browser.

If the problem persists after these corrections, it may be necessary to move on to further troubleshooting steps.

Clear Your Browser’s Cache & Cookies 

Over time, your browser stores temporary data, including cache & cookies, to help websites load faster. However, if this data gets too large, corrupted, or outdated, it can cause issues like the 400 Bad Request Cookie Too Large error. In this case, clearing your browser’s cache and cookies can fix the problem by forcing the browser to load a fresh website version. 

We’ve already learned how to clear browser data in different web browsers. You will find all the information you need in the following tutorial:

– How to Clear Browser Cache and Cookies in Chrome, Edge, and Firefox

Once you clear your browser data, websites may take slightly longer to load the first time, as your browser has to re-download site files. You may also need to log in again to websites that require authentication. However, this process refreshes your connection, often resolving the 400 error. 

If clearing the browser cache and cookies does not fix the issue, move on to the next troubleshooting step to further diagnose the problem.

Deactivate Browser Extensions

Browser extensions add extra features to your browser; however, some extensions can interfere with how websites load, causing errors like the 400 Bad Request – Request Header or Cookie Too Large error. If an extension modifies your browser’s requests or blocks scripts, it can prevent the website from loading correctly. 

To check if an extension is causing the error, try opening the website in Incognito Mode (Private Browsing Mode). Most browsers disable extensions in this mode, so if the website loads correctly, an extension is likely the problem. 

In this case, you need to disable extensions. We’ve already covered this step-by-step in the following guide:

– How to Disable Browser Extensions

If disabling extensions fixes the 400 error, you can try updating the problematic extension or finding an alternative. If the error persists after disabling extensions, move on to the next troubleshooting step.

Flush the DNS Cache

Your computer stores Domain Name System (DNS) records to help websites load faster. This stored data, called the DNS cache, allows your browser to find websites fast without looking them up every time. However, if the cache becomes outdated or corrupted, it can cause issues, including the 400 Bad Request – Request Header or Cookie Too Large error.

In this situation, flushing the DNS cache removes this old data and forces your computer to fetch fresh information from the server, which can help fix the problem. Here’s how you can do it on a Windows computer:

Click Start and type cmd in the search bar. Next, right-click Command Prompt and select Run as administrator.

You may be prompted to confirm if you want to allow this app to make changes to your device. Click Yes to continue. Once the Windows Command Prompt window is opened, type the following command: 

ipconfig /flushdns

Then, press Enter, and you should see a message saying, Successfully flushed the DNS Resolver Cache.

After that, restart your web browser and try re-accessing the website. 

TIP: Mac users can type sudo killall -HUP mDNSResponder and Linux users can write sudo systemd-resolve –flush-caches on the terminal to clear DNS cache.

If flushing the DNS cache doesn’t fix the error, move to the next solution.

Check File Size & Compress If Needed

Sometimes, the request header or cookie too large issue arises when the file you’re trying to upload is larger than the server allows. This limitation is in place to ensure server performance and security. If you encounter a 400 error during an upload, the first step is to consider the size of your file.

To determine if file size is the problem, try uploading a smaller file. If the smaller file uploads without any issues, it’s likely that your original file is too big. This test helps confirm the root cause of the error without going into more complex diagnostics.

If your file is too large, reduce its size. Depending on the type of file you are dealing with, there are several approaches you can take:

For images, tools like TinyPNG.com can reduce file size without significantly compromising quality.

You can also refer to the following tutorial to optimize images:

– WordPress Image Optimization Techniques For Faster Loading

Videos can be compressed using applications like HandBrake.fr that reduce video size.

Similarly, audio files can be managed through Media.io, which reduces the file size without losing clarity.

By testing with smaller files and using online tools to compress larger ones, you can effectively manage your uploads and avoid this issue. Always check the server’s file size limits before uploading to ensure a smooth process.

FAQS

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