To set up custom error pages in IIS, first enable custom errors in the web.config file under the section, then specify each status code with its corresponding error page. 1. Edit the web.config file within your site root or application folder. 2. Set errorMode to "Custom" and define error entries for codes like 404 and 500 using the responseMode "ExecuteURL" to ensure correct HTTP status codes. 3. Create user-friendly error pages with clear messages, navigation options, branding, and appropriate suggestions based on the error type. 4. Verify that each error page returns the correct HTTP status code without causing redirects or infinite loops. 5. Test manually using invalid URLs or tools like Fiddler, Postman, or curl to confirm functionality and prevent issues caused by dynamic modules like URL Rewrite.

When you're running a website on IIS (Internet Information Services), having custom error pages for different HTTP status codes is a good way to improve user experience and help with SEO. Instead of showing the default, often unhelpful or even confusing error messages, you can guide users back on track or at least explain what went wrong.

Here’s how to set it up effectively without getting stuck in technical jargon.

How IIS Handles Errors by Default

Out of the box, IIS has its own generic error pages for common HTTP status codes like 404 (Not Found), 500 (Internal Server Error), and others. These are usually plain and not branded or helpful from an end-user perspective.

By default, IIS uses two main settings:

• Detailed errors – useful for developers during debugging
• Custom errors – what visitors see when something goes wrong

Most production sites should switch to "custom errors" and provide their own branded pages.

Setting Up Custom Error Pages in web.config

To configure custom error pages, you typically edit the web.config file in your site root or application folder. This method works well for ASP.NET apps and static sites hosted in IIS.

Inside <system.webserver></system.webserver>, use the <httperrors></httperrors> section like this:

<configuration>
  <system.webServer>
    <httpErrors errorMode="Custom">
      <remove statusCode="404" />
      <error statusCode="404" path="/errors/404.html" responseMode="ExecuteURL" />
      <remove statusCode="500" />
      <error statusCode="500" path="/errors/500.html" responseMode="ExecuteURL" />
    </httpErrors>
  </system.webServer>
</configuration>

A few notes here:

• Make sure your custom error files exist and are accessible.
• Use responseMode="ExecuteURL" if you want server-side processing (like ASPX pages).
• If using static HTML, that's fine too—just make sure paths are correct.

You can add as many status codes as needed using the same pattern.

Creating Useful Custom Error Pages

Just replacing the page isn’t enough—you want them to be helpful. Here’s what to include:

• A clear message explaining the error
• Navigation options or a search bar
• Your logo or branding
• Optionally, a link to your homepage or support contact

For example:

• 404 Page: Suggest popular pages or categories, maybe a search box
• 500 Page: Apologize and suggest trying again later; offer email support

Also, ensure these pages return the correct HTTP status code. It’s easy to mess this up if you’re redirecting instead of executing the URL directly.

Testing Your Setup

Once configured, always test each error page manually to confirm:

• The right page shows up
• The correct HTTP status code is returned
• No infinite loops occur (e.g., if your error page itself triggers an error)

You can use tools like Fiddler, Postman, or even curl to check headers. Or just visit known bad URLs for 404 testing.

If you're dealing with dynamic content or modules like URL Rewrite, double-check that they don’t interfere with error handling.

That's about it — it’s not overly complex but does require attention to detail. With a little setup, your site looks more professional and handles hiccups gracefully.

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