How do you get the MIME type of a file in C#?

Question

Anubhav Kumar · Answer

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, extensibleRequires: 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 useLimitations: 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:
MimeDetectiveHeyRed.Mime
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
and 
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How do you get the MIME type of a file in C#?

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1 Answers

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

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

3. Use `Registry` (Windows-only)

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

Summary

Liked By

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