What Is System Web Server in Web Config?


Larry Thompson

When it comes to configuring a web application, the web.config file plays a crucial role. It is responsible for specifying various settings that determine how the application behaves and handles requests.

One important element within the web.config file is the System.WebServer element. In this article, we will explore what the System.WebServer element is and how it can be used in web.config.

Understanding System.WebServer

The System.WebServer element is a section within the web.config file that allows you to configure settings related to IIS (Internet Information Services) and how your application interacts with the server. It provides a way to fine-tune how IIS handles requests, manages resources, and handles various aspects of web hosting.

The Importance of System.WebServer

The System.WebServer section gives you granular control over various settings related to IIS. Some of the key areas that can be configured include:

  • MimeMap: This allows you to specify mappings between file extensions and MIME types. For example, you can define that files with a .pdf extension should be served with the “application/pdf” MIME type.
  • Caching: You can configure caching rules for different types of content.

    This helps improve performance by caching static files or controlling how dynamic content is cached.

  • Error Pages: You can specify custom error pages for different HTTP status codes, providing a better user experience when errors occur.
  • URL Rewrite: This feature allows you to define rewrite rules for URLs. You can redirect or rewrite URLs based on specific patterns.

Examples of System.WebServer Usage

Let’s take a look at a couple of examples to understand how the System.WebServer element can be used in web.

Example 1: Configuring MimeMap

To define a custom mapping between a file extension and MIME type, you can add the following code within the System.WebServer section:

      <mimeMap fileExtension=".docx" mimeType="application/vnd.openxmlformats-officedocument.wordprocessingml.document" />

In this example, any file with the .docx extension will be served with the “application/vnd.document” MIME type.

Example 2: Configuring URL Rewrite

If you want to rewrite URLs based on specific patterns, you can use the <rewrite> element within the <system.webServer> section. Here’s an example:

        <rule name="Rewrite to index.php">
          <match url="^(.*)$" />
          <action type="Rewrite" url="index.phpurl={R:1}" />

In this example, all incoming requests will be rewritten to the index.php file, and the original URL will be passed as a query parameter.


The System.WebServer element in the web.config file is a powerful tool for configuring various aspects of how your web application interacts with IIS. It allows you to customize settings related to MIME types, caching, error pages, URL rewriting, and more. By leveraging this element effectively, you can optimize the performance and behavior of your web application.

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