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Home Forums How do you get the MIME type of a file in C#? – MindStick
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1 Answers

Anubhav Sharma
Anubhav Sharma 23 May 2025
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In C#, there are several ways to determine the MIME type of a file. Here are the most common approaches:

1. Use Microsoft.AspNetCore.StaticFiles.FileExtensionContentTypeProvider (Recommended in ASP.NET Core)

using Microsoft.AspNetCore.StaticFiles;

var provider = new FileExtensionContentTypeProvider();
if (!provider.TryGetContentType("example.pdf", out string contentType))
{
    contentType = "application/octet-stream"; // default fallback
}
Console.WriteLine(contentType); // Outputs: application/pdf
  • Pros: Reliable, easy, extensible
  • Requires: Microsoft.AspNetCore.StaticFiles NuGet package

2. Use Windows Registry via System.Web.MimeMapping (Only on Windows / ASP.NET)

string mimeType = System.Web.MimeMapping.GetMimeMapping("file.docx");
Console.WriteLine(mimeType); // Outputs: application/vnd.openxmlformats-officedocument.wordprocessingml.document
  • Pros: Simple to use
  • Limitations: Windows-only, available only in .NET Framework (not .NET Core)

3. Use Registry (Windows-only)

using Microsoft.Win32;

string GetMimeType(string fileName)
{
    string extension = Path.GetExtension(fileName)?.ToLowerInvariant();
    if (extension == null) return "application/octet-stream";

    RegistryKey key = Registry.ClassesRoot.OpenSubKey(extension);
    return key?.GetValue("Content Type") as string ?? "application/octet-stream";
}

Platform-specific — Windows only.

4. Use File Content (Magic Numbers) with MimeDetective (Advanced)

If you want to inspect the actual file content (not just the extension), use third-party libraries like:

Example using MimeDetective:

using MimeDetective;

var inspector = new ContentInspectorBuilder()
    .AddDefaults()
    .Build();

var fileInfo = new FileInfo("example.png");
var result = inspector.Inspect(fileInfo);
Console.WriteLine(result?.MimeType); // Outputs: image/png

Best for file content validation (e.g., to detect forged extensions)

Summary

Method Works in .NET Core Platform Based on Accuracy
FileExtensionContentTypeProvider Yes Cross-platform File extension Medium
System.Web.MimeMapping No Windows only (.NET Framework) File extension Medium
Registry access NO Windows only File extension Medium
MimeDetective or HeyRed.Mime Yes Cross-platform File content High

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