MCP Multi-Language Sandbox

Execute code securely in 6 programming languages with Docker isolation, designed for Claude Code via Model Context Protocol (MCP).

What is this?

A local MCP server that lets Claude execute code in isolated Docker containers. Think of it as your own private code sandbox - 100% free, 100% local, no cloud dependencies.

Why use this instead of cloud sandboxes?

• Free: No per-execution costs (vs ~$0.10/run on cloud services)
• Fast: 0ms container acquisition with pooling (vs 2-5s cold starts)
• Private: Code never leaves your machine
• Customizable: Add your own languages, packages, security rules

Features

• 6 Languages: Python, TypeScript, JavaScript, Go, Rust, Bash
• Container Pooling: Pre-warmed containers for instant execution
• Package Caching: Install once, reuse forever (SHA256-based)
• ML Runtime: numpy, pandas, sklearn, torch, mlx pre-installed
• Security: Seccomp profiles, capability dropping, audit logging
• Sessions: Persistent state with TTL and auto-cleanup

Quick Start

Prerequisites

• Node.js >= 18.0.0
• Docker Desktop
• Claude Code CLI (optional, for MCP integration)

Installation

# Clone the repository
git clone https://github.com/Pit-CL/mcp-multilang-sandbox.git
cd mcp-multilang-sandbox

# Install dependencies
npm install

# Build
npm run build

# Run tests (optional)
npm run test:mcp

Add to Claude Code

# Add as MCP server
claude mcp add multilang-sandbox node /path/to/mcp-multilang-sandbox/dist/mcp/server.js

# Verify it's connected
claude mcp list
# Should show: multilang-sandbox ✓ Connected

Manual Configuration

Add to your Claude settings (~/.claude.json or VS Code settings):

{
  "mcpServers": {
    "multilang-sandbox": {
      "command": "node",
      "args": ["/path/to/mcp-multilang-sandbox/dist/mcp/server.js"],
      "env": {
        "LOG_LEVEL": "info"
      }
    }
  }
}

Usage

Once configured, Claude can use these tools:

Execute Code

// Python
sandbox_execute({ language: 'python', code: 'print("Hello!")' })

// TypeScript
sandbox_execute({ language: 'typescript', code: 'console.log("Hello!")' })

// With ML libraries (numpy, pandas, sklearn, torch)
sandbox_execute({
  language: 'python',
  code: 'import numpy as np; print(np.array([1,2,3]))',
  ml: true
})

Persistent Sessions

// Create a session
sandbox_session({ action: 'create', name: 'my-project', language: 'python' })

// Execute in session (state persists)
sandbox_execute({ language: 'python', code: 'x = 42', session: 'my-project' })
sandbox_execute({ language: 'python', code: 'print(x)', session: 'my-project' })  // prints 42

// Install packages
sandbox_install({ session: 'my-project', packages: ['pandas', 'requests'] })

// Cleanup
sandbox_session({ action: 'destroy', name: 'my-project' })

File Operations

// Write a file
sandbox_file_ops({ session: 'my-project', operation: 'write', path: 'data.csv', content: 'a,b\n1,2' })

// Read it back
sandbox_file_ops({ session: 'my-project', operation: 'read', path: 'data.csv' })

System Stats

// View pool, cache, and session stats
sandbox_inspect({ target: 'all' })

// Security audit
sandbox_security({ action: 'stats' })

MCP Tools Reference

Tool	Description
sandbox_execute	Execute code in any supported language
sandbox_session	Create/list/pause/resume/destroy sessions
sandbox_install	Install packages with caching
sandbox_file_ops	Read/write/list/delete files in sessions
sandbox_inspect	View system stats (pool, cache, sessions)
sandbox_security	View audit logs and security events

Architecture

┌─────────────────────────────────────────────────────────┐
│                    Claude / MCP Client                   │
└───────────────────────────┬─────────────────────────────┘
                            │ JSON-RPC (stdio)
┌───────────────────────────▼─────────────────────────────┐
│                    MCP Sandbox Server                    │
│  ┌────────────────────────────────────────────────────┐ │
│  │  Tools: execute | session | install | file_ops     │ │
│  │         inspect | security                          │ │
│  ├────────────────────────────────────────────────────┤ │
│  │  Core: ContainerPool | PackageCache | Sessions     │ │
│  ├────────────────────────────────────────────────────┤ │
│  │  Security: Seccomp | Capabilities | AuditLogger    │ │
│  ├────────────────────────────────────────────────────┤ │
│  │  Runtimes: Python | TS | JS | Go | Rust | Bash     │ │
│  └────────────────────────────────────────────────────┘ │
└───────────────────────────┬─────────────────────────────┘
                            │ Dockerode
┌───────────────────────────▼─────────────────────────────┐
│                      Docker Engine                       │
│    [Container Pool]  [Active Sessions]  [Image Cache]   │
└─────────────────────────────────────────────────────────┘

Security

6 Layers of Protection

1. Code Validation - Pattern blocklist (os, subprocess, eval, exec)
2. Seccomp Profiles - Syscall filtering per language
3. Capability Dropping - CAP_DROP ALL
4. Network Isolation - NetworkMode: none
5. Resource Limits - Memory, CPU, PIDs, ulimits
6. Audit Logging - All operations tracked

Blocked Syscalls

ptrace, mount, umount, kexec_load, init_module, delete_module, reboot, bpf, userfaultfd, and more

Performance

Metric	Value
Pool hit (warm)	0ms
Pool miss (cold)	~80-100ms
Session create	~85ms
Package cache hit	<1ms
Python execution	~60ms
Bash execution	~35ms

Development

# Watch mode (auto-rebuild)
npm run dev

# Type checking
npm run typecheck

# Run tests
npm run test:all        # All tests
npm run test:mcp        # MCP tools (19 tests)
npm run test:runtimes   # Language runtimes

# Clean build
npm run clean && npm run build

Project Structure

src/
├── mcp/server.ts           # MCP server & tool handlers
├── core/
│   ├── ContainerPool.ts    # Pre-warmed container pooling
│   ├── PackageCache.ts     # SHA256-based package caching
│   └── SessionManager.ts   # Persistent sessions with TTL
├── security/
│   ├── seccomp.ts          # Syscall filtering profiles
│   └── AuditLogger.ts      # Operation audit logging
├── runtimes/
│   ├── PythonRuntime.ts    # + PythonMLRuntime for ML
│   ├── TypeScriptRuntime.ts
│   ├── JavaScriptRuntime.ts
│   ├── GoRuntime.ts
│   ├── RustRuntime.ts
│   └── BashRuntime.ts
└── docker/
    ├── DockerClient.ts     # Dockerode wrapper
    └── Container.ts        # Container abstraction

Contributing

Issues and PRs welcome! This started as a personal project to replace cloud sandboxes with something local and free.

License

MIT

Credits

Built with @modelcontextprotocol/sdk, Dockerode, and Zod.