When working with SVG files in ASP.NET applications during Visual Studio debugging sessions, you might encounter this behavior:

<!-- Works in static HTML -->
<img src="image.svg" alt="SVG should appear" />

<!-- Fails in ASPX page -->
<img src="image.svg" alt="Broken image shown" />

Fiddler reveals the core issue - the Development Server sends SVG files with incorrect MIME type:

HTTP/1.1 200 OK
Content-Type: application/octet-stream  <-- Wrong MIME type

Instead of the required image/svg+xml, Visual Studio's built-in web server defaults to generic binary format.

1. IIS Configuration (For Production)

Ensure proper MIME type mapping in IIS Manager:

Extensions: .svg
MIME Type: image/svg+xml

2. Visual Studio Development Server Fix

Add this to your Web.config to override the default behavior:

<system.webServer>
  <staticContent>
    <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
    <mimeMap fileExtension=".svgz" mimeType="image/svg+xml" />
  </staticContent>
</system.webServer>

3. Alternative Solution Using IIS Express

Modify applicationhost.config (typically in Documents\IISExpress\config):

<staticContent lockAttributes="isDocFooterFileName">
  <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
</staticContent>

Always verify with browser developer tools:

1. Check Network tab for correct Content-Type header
2. Ensure no caching issues (use Ctrl+F5)
3. Validate SVG file syntax at https://validator.w3.org

For dynamic SVG generation:

protected void Page_Load(object sender, EventArgs e)
{
    Response.ContentType = "image/svg+xml";
    Response.Write("<svg xmlns='http://www.w3.org/2000/svg'>...</svg>");
    Response.End();
}

---

When working with SVG files in ASP.NET projects, developers often encounter this frustrating scenario:

<img src="document_edit.svg" alt="SVG not displaying" />

The image shows fine when testing as static HTML, but fails when running through Visual Studio's development server. Fiddler reveals the core issue:

Content-Type: application/octet-stream

The ASP.NET Development Server (Cassini) and IIS Express don't automatically recognize SVG files, even when:

• MIME types are properly configured in IIS Manager
• The registry contains correct SVG MIME type entries
• The web.config includes staticContent mappings

For IIS Express (Visual Studio 2015+)

Add this to your web.config:

<system.webServer>
  <staticContent>
    <remove fileExtension=".svg" />
    <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
    <remove fileExtension=".svgz" />
    <mimeMap fileExtension=".svgz" mimeType="image/svg+xml" />
  </staticContent>
</system.webServer>

For Classic ASP.NET Development Server

Create an HTTP handler in web.config:

<system.web>
  <httpHandlers>
    <add verb="*" path="*.svg" 
         type="System.Web.StaticFileHandler" />
  </httpHandlers>
</system.web>

If SVGs still won't display, check these potential culprits:

// Sample C# code to verify MIME type in Application_Start
var svgMime = MimeMapping.GetMimeMapping("test.svg");
Debug.WriteLine(svgMime); // Should output "image/svg+xml"

For IIS 10 specific cases, you might need to modify the applicationHost.config:

<location path="Default Web Site">
  <system.webServer>
    <staticContent>
      <mimeMap fileExtension=".svg" mimeType="image/svg+xml" />
    </staticContent>
  </system.webServer>
</location>

As a temporary workaround, you can use data URIs:

<img src="data:image/svg+xml;base64,[base64-encoded-svg]" 
     alt="Embedded SVG" />

Or serve the SVG through a handler:

public class SvgHandler : IHttpHandler
{
    public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "image/svg+xml";
        context.Response.WriteFile(context.Request.PhysicalPath);
    }
}