ILSpy MCP Server

A production-grade MCP server that exposes all major ILSpy CLI features as separate tools for decompiling .NET assemblies.

Features

• 10 MCP Tools: Decompile, export projects, extract IL, list types/methods, resolve references, and more
• Workflow Orchestration: Automated end-to-end processing of .NET assemblies
• Structured Output: JSON reports with metadata, types, methods, and logs
• Forward Compatible: Raw ilspycmd tool for unsupported features
• Cross-Platform: Works on Windows, Linux, and macOS

Prerequisites

• Python 3.10+
• ILSpy CLI (ilspycmd) installed and available in PATH
  • Download from: https://github.com/icsharpcode/ILSpy/releases
  • Or install via: dotnet tool install -g ilspycmd

Installation

pip install -r requirements.txt

Usage

Option 1: MCP Server Mode

Start the MCP server and use it with any MCP-compatible client:

python server.py

The server communicates via stdio using JSON-RPC. Configure it in your MCP client using config.json.

Option 2: Direct Orchestrator Usage

Process assemblies directly using the orchestrator:

# Single assembly
python orchestrator.py assembly.dll

# Multiple assemblies
python orchestrator.py assembly1.dll assembly2.dll assembly3.exe

# With options
python orchestrator.py assembly.dll --langver:11 --nullable --no-records

Option 3: Python API

Use the orchestrator programmatically:

from orchestrator import process_assemblies, save_report
from pathlib import Path

report = process_assemblies(
    ["assembly.dll"],
    language_version="11",
    nullable_enabled=True,
    handle_records=True,
)

save_report(report, Path("work/report.json"))

Tools

1. decompile_file - Decompile assembly to C# files

   • Supports: --langver, --nullable, --with-records, etc.

2. export_project - Export compilable C# project

   • Includes: References, metadata, project files

3. get_il - Extract IL code

   • View intermediate language instead of decompiled C#

4. list_types - List all types in assembly

   • Returns: Namespace-qualified type names

5. list_methods - List methods for a type

   • Input: Full type name (e.g., Namespace.ClassName)

6. resolve_references - Analyze external references

   • Extracts: Package references, assembly references

7. set_language_version - Control C# language version

   • Versions: 9, 10, 11, 12, etc.

8. enable_nullable_context - Enable/disable nullable reference types

   • Options: true or false

9. handle_records_init_only - Handle record types properly

   • Ensures: Records and init-only setters decompile correctly

10. raw_ilspycmd - Run arbitrary ilspycmd commands

    • Forward-compatible with all future ILSpy features

Output Structure

work/
  input/              # Input assemblies (optional)
  output/
    decompile/        # Decompiled C# files
      <assembly>/
        *.cs files
    project/          # Exported projects
      <assembly>/
        *.csproj
        *.cs files
    il/               # IL code output
      <assembly>/
        *.il files
  report.json         # Final structured JSON report

JSON Report Format

The orchestrator generates a structured JSON report:

{
  "assemblies": [
    {
      "assembly": "example.dll",
      "status": "success",
      "paths": {
        "decompiled": "work/output/decompile/example/",
        "project": "work/output/project/example/",
        "il": "work/output/il/example/"
      },
      "types": [
        {
          "name": "Namespace.MyClass",
          "methods": ["Main", "DoSomething"],
          "il_size": {"Main": 123, "DoSomething": 42}
        }
      ],
      "references": ["System", "System.Linq"],
      "flags_used": ["--langver:11", "--nullable"],
      "logs": {
        "stdout": "...",
        "stderr": "..."
      }
    }
  ]
}

Workflow

The orchestrator follows this workflow for each assembly:

1. Decompile → Generate C# source files
2. Export Project → Create compilable project with references
3. Extract IL → Get intermediate language code
4. List Types → Discover all types in assembly
5. List Methods → For each type, extract methods
6. Resolve References → Analyze dependencies
7. Apply Settings → Language version, nullable context, records
8. Generate Report → Collect all metadata into JSON

Error Handling

• All tools return structured JSON with returncode, stdout, and stderr
• Failed operations are marked with status: "error" in the report
• Full error logs are included in the report for debugging
• Tools are idempotent - safe to run multiple times

Examples

See example_usage.py for complete examples of:

• Processing single assemblies
• Processing multiple assemblies
• Using different language versions
• Enabling/disabling nullable context
• Custom flags and options

License

This project wraps ILSpy CLI. Please refer to ILSpy's license for usage terms.