How to Fix HTTP Error 400: Request Header Field Too Long

Encountering the “HTTP Error 400: Request Header Field Too Long” can be frustrating. This error indicates that the server is refusing to process your request because one or more of the HTTP request headers are exceeding the server’s configured size limit. This typically happens due to excessively large cookies or overly long URLs. Here’s a comprehensive guide to diagnosing and resolving this issue.

Understanding the “400 Bad Request” Error

The HTTP 400 Bad Request error is a client-side error, meaning the issue originates from the client’s request, not the server itself. When the server encounters a request that it cannot understand or process, it returns a 400 error. In the specific case of “Request Header Field Too Long”, the problem lies in the size of the headers being sent.

Common Causes

  • Excessive Cookies: Cookies store information about your browsing activity and preferences. Over time, they can accumulate, and if some become unusually large (or you have too many), they can cause the total header size to exceed the limit.
  • Large URLs: GET requests often include parameters appended to the URL. If the URL becomes exceptionally long due to numerous or lengthy parameters, it can trigger the error.
  • Browser Extensions: Some browser extensions can inject headers into requests, contributing to the overall size.
  • Server Configuration: Although less common, the server might have a very restrictive limit on header size.

Troubleshooting Steps

Here’s a step-by-step approach to resolve the “HTTP Error 400: Request Header Field Too Long” error:

1. Clear Browser Cookies

The most frequent culprit is oversized cookies. Clearing your browser’s cookies is the first and most crucial step. Here’s how to do it for popular browsers:

  • Chrome:
    • Click the three dots (menu) in the top right corner.
    • Go to “More tools” > “Clear browsing data”.
    • Select “Cookies and other site data”.
    • Choose “All time” for the time range.
    • Click “Clear data”.
  • Firefox:
    • Click the three horizontal lines (menu) in the top right corner.
    • Go to “Options” > “Privacy & Security”.
    • Under “Cookies and Site Data”, click “Clear Data”.
    • Ensure “Cookies and Site Data” is checked.
    • Click “Clear”.
  • Safari:
    • Go to “Safari” > “Preferences” > “Privacy”.
    • Click “Manage Website Data”.
    • Click “Remove All”.

After clearing cookies, restart your browser and try accessing the website again.

2. Clear Browser Cache

While cookies are the primary suspect, clearing the browser cache can also help, as it removes potentially outdated or corrupted files that might be contributing to the issue.

  • Chrome: (Same as clearing cookies, but select “Cached images and files” instead of “Cookies and other site data”)
  • Firefox: (Same as clearing cookies, but select “Cached Web Content” instead of “Cookies and Site Data”)
  • Safari: Go to “Safari” > “Clear History” and choose a time range.

3. Check for Problematic Browser Extensions

Disable browser extensions one by one to see if any are causing the issue. Here’s how:

  • Chrome:
    • Type chrome://extensions in the address bar and press Enter.
    • Toggle off each extension individually and test the website.
  • Firefox:
    • Type about:addons in the address bar and press Enter.
    • Disable each extension individually and test the website.
  • Safari:
    • Go to “Safari” > “Preferences” > “Extensions”.
    • Uncheck each extension individually and test the website.

If disabling a specific extension resolves the error, consider removing or updating the extension.

4. Try a Different Browser

To isolate the problem, try accessing the website using a different browser. If the error doesn’t occur in another browser, it indicates that the issue is specific to your original browser’s configuration or extensions.

5. Investigate the URL (If Applicable)

If the error occurs when accessing a specific URL with many parameters, try shortening the URL or using a different method to pass the data (e.g., POST request instead of GET). Long URLs are less common causes, but should be checked if they are applicable.

6. Server-Side Considerations (For Website Owners/Administrators)

If you are the website owner or administrator, you might need to adjust your server’s configuration to allow larger header sizes. The specific configuration depends on your web server (e.g., Apache, Nginx, IIS).

  • Apache: Modify the LimitRequestFieldSize directive in your Apache configuration file (e.g., httpd.conf or .htaccess).
  • Nginx: Adjust the large_client_header_buffers directive in your Nginx configuration file (e.g., nginx.conf).
  • IIS: Modify the maxAllowedContentLength attribute in the system.webServer/security/requestFiltering/requestLimits section of your web.config file.

Important: Increasing header size limits can potentially expose your server to security risks. Ensure you understand the implications before making changes.

7. Contact Website Support

If none of the above steps resolve the issue, contact the website’s support team. They may be experiencing server-side problems or have specific recommendations for your situation.

Conclusion

The “HTTP Error 400: Request Header Field Too Long” error is typically caused by excessive cookies. Clearing cookies, cache, and disabling browser extensions are the most common solutions. If the problem persists, consider trying a different browser or contacting the website’s support team. Website owners might need to adjust their server configuration to allow larger header sizes, but this should be done cautiously.