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Pit-CL

MCP Multi-Language Sandbox

by Pit-CL
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TypeScript
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MCP Multi-Language Sandbox

TypeScript MCP License: MIT Tests

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

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.

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