How to Force WWW in Your ASP.NET Website Using Global.asax

In ASP.NET, you can easily enforce this redirect using code in the Global.asax file.

✅ When to Use This

• You're managing an ASP.NET Web Forms or MVC site.

• You want to enforce a www-only version of your domain for SEO, branding, and SSL consistency.

• You're not using a reverse proxy or external redirect rules (like in IIS or a CDN).

🛠 Code to Force WWW in Global.asax.cs

Add the following code to the Application_BeginRequest method:

protected void Application_BeginRequest(object sender, EventArgs e)
{
    // Ensure the request starts with "www" and is not localhost (for development)
    if (!Request.Url.Host.StartsWith("www") && !Request.Url.IsLoopback)
    {
        // Redirect to the www version
        UriBuilder builder = new UriBuilder(Request.Url);
        builder.Host = "www." + Request.Url.Host;
        Response.Redirect(builder.ToString(), true);
    }
}

💡 How It Works

• ✅ Runs at the beginning of every request.

• ✅ Checks if the request is missing “www”.

• ✅ Skips redirects for localhost (useful during development).

• ✅ Redirects to the www version using a 302 redirect (or 301 if you prefer).

🔁 Optional: Make Redirect Permanent (301)

To enforce a permanent redirect for SEO:

Response.Redirect(builder.ToString(), true); // Temporary (302)
// Replace with:
Response.RedirectPermanent(builder.ToString()); // Permanent (301)

🧠 Best Practices

• Ensure your SSL certificate covers both www and non-www domains (or use a wildcard certificate).

• Only implement this redirect in one place (Global.asax or IIS or CDN) to avoid conflicts.

• For larger websites or multi-domain setups, consider implementing this rule at the server level (IIS or load balancer)