DLL Decompiler MCP Server

A Model Context Protocol (MCP) server that decompiles .NET DLL assemblies using ICSharpCode.Decompiler (ILSpy’s library) and exposes the decompiled code to AI tools.

Features

• Decompilation: Decompiles .NET DLLs to C# source code
• Caching: Persistent file-based caching using SHA256 hash for speed
• Search: Search across all decompiled code
• Resources: Exposes decompiled files as MCP resources
• Tools: Provides MCP tools for decompilation and search operations

Installation

Prerequisites

• .NET 9.0 SDK or later
• Windows, Linux, or macOS

Build

cd c:\development\mcpeek\McPeek
dotnet build

Usage

Running the Server

dotnet run

The server communicates via stdio and follows the MCP protocol.

MCP Tools

The server exposes the following tools:

1. DecompileFolder

Decompiles all .NET DLL files in a specified folder.

Parameters:

• folderPath (string): The absolute path to the folder containing DLL files

Returns:

{
  "Success": true,
  "Message": "Successfully decompiled 5 assemblies",
  "AssemblyNames": ["Assembly1", "Assembly2", ...],
  "TotalFiles": 150
}

2. DecompileDll

Decompiles a specific DLL file.

Parameters:

• dllPath (string): The absolute path to the DLL file

Returns:

{
  "Success": true,
  "Message": "Successfully decompiled MyAssembly",
  "AssemblyNames": ["MyAssembly"],
  "TotalFiles": 30
}

3. SearchCode

Searches for text patterns across all decompiled C# code.

Parameters:

• query (string): The text to search for
• caseSensitive (bool, optional): Whether search should be case-sensitive (default: false)
• maxResults (int, optional): Maximum number of results to return (default: 50)

Returns:

{
  "Success": true,
  "Query": "MyClass",
  "TotalMatches": 10,
  "Results": [
    {
      "AssemblyName": "MyAssembly",
      "FilePath": "MyNamespace/MyClass.cs",
      "LineNumber": 42,
      "LineContent": "public class MyClass",
      "Context": "..."
    }
  ]
}

4. ListLoadedAssemblies

Lists all assemblies that have been decompiled and are currently loaded.

Returns:

{
  "Success": true,
  "TotalAssemblies": 5,
  "Assemblies": [
    {
      "Name": "MyAssembly",
      "Path": "C:\\path\\to\\MyAssembly.dll",
      "FileCount": 30,
      "DecompiledAt": "2025-10-24T12:00:00Z"
    }
  ]
}

5. GetCacheStatistics

Gets statistics about the decompilation cache.

Returns:

{
  "Success": true,
  "TotalCachedAssemblies": 10,
  "CacheDirectory": "C:\\Users\\...\\Temp\\McPeek\\cache",
  "CacheSizeMB": 15.5
}

6. ClearCache

Clears all cached decompilation results.

Returns:

{
  "Success": true,
  "Message": "Cache cleared successfully"
}