top of page

How to Fix HTTP Error 400: The size of the request headers is too long while opening SharePoint

HTTP Error 400 is a common issue encountered when working with SharePoint Online and Office 365. This error occurs when the size of the request headers exceeds the maximum limit allowed by the server. In this article, we will guide you on how to fix HTTP Error 400: The size of the request headers is too long which comes in Google Chrome while opening the SharePoint Online Office 365 site.

Bad Request – Request Too Long

HTTP Error 400. The size of the request headers is too long

When the server receives a request with headers that exceed the allowed size limit, it responds with the HTTP Error 400 status code, indicating that the request is invalid due to excessive header size.

How to Fix HTTP Error 400

This error can disrupt the normal functioning of SharePoint Online and Office 365 services, leading to restricted access, failed operations, or unexpected behavior.

Causes of HTTP Error 400

Below are some of the reasons which can cause HTTP Error 400 to occur:

1. Large Number of Cookies:

One of the primary causes of the error is having an excessive number of cookies stored in the browser. Each cookie adds to the size of the request headers, and when the cumulative size exceeds the limit, the error occurs.

2. Excessive Request Headers:

Including too many headers in the request can also trigger the error. Headers such as authorization, user agent, and custom headers contribute to the overall size of the request, and if they surpass the allowed limit, an error is encountered.

3. Malformed or Corrupted Headers:

In some cases, the error may be caused by malformed or corrupted headers in the request. Incorrectly formatted or invalid headers can lead to the request being rejected by the server.

How to Fix HTTP Error 400: The size of the request headers is too long while opening SharePoint

The easiest way to resolve this error is to clear browser cookies. Follow the below steps to clear the browser cookies:

STEP 1: Open Google Chrome settings. On the left pane, click on "Privacy and Security".

How to Fix HTTP Error 400 (1)

STEP 2: Now, in Privacy and Security, click on “Clear browsing data”.

How to Fix HTTP Error 400 (2)

STEP 3: Now, you have to select the Time range “All time” and then click on “Clear Data”. See the below image.

How to Fix HTTP Error 400 (4)

STEP 4: Now open the SharePoint online URL, you will not get the error “HTTP Error 400. The size of the request headers is too long”.

Best Practices to Prevent the HTTP Error 400

The HTTP Error 400 can be frustrating for both website users and developers. It occurs when the client sends a request to the server that the server cannot understand or process. To ensure a seamless browsing experience and prevent encountering this error, it is essential to follow best practices when crafting and handling HTTP requests.

Best Practice 1: Managing Cookies and Headers Efficiently

Regularly managing and clearing browser cookies can help prevent the accumulation of unnecessary cookies that contribute to the header size. Additionally, being mindful of the headers included in requests and minimizing their usage can also aid in preventing errors.

Best Practice 2: Streamlining Request Header Usage

Consider reviewing the application or system architecture to ensure efficient utilization of request headers. Avoid including redundant or excessive header information and focus on including only essential headers.

Best Practice 3: Monitoring and Testing for Potential Issues

Regularly monitor and test the application or system to identify any potential header-related issues. Implementing automated testing and performance monitoring can help proactively detect and address header size problems.

By adhering to these practices, you can minimize the occurrence of HTTP Error 400 and enhance the overall reliability and performance of your web applications.


In conclusion, encountering the "The size of the request headers is too long" error in SharePoint Online and Office 365 can be frustrating, but with proper understanding and implementation of the suggested solutions and best practices, it can be effectively resolved. By managing cookies, optimizing header usage, and being mindful of server limits, you can ensure smoother operations and a better user experience.



bottom of page