descoped/mcp-pkg-local

mcp-pkg-local

An MCP (Model Context Protocol) server that enables LLMs to read and understand locally installed package source code, helping reduce API hallucinations by providing direct access to actual installed packages.

Features

Core Capabilities

• 🔍 Auto-Detection: Automatically detects Python or Node.js projects
• 📖 Source Code Access: Direct reading of actual installed package source code
• ⚡ High Performance: SQLite cache with 40x faster validity checks
• 🎯 Zero Configuration: Works immediately with standard project structures
• 🚀 Production Ready: 300+ tests, 14 CI stages, comprehensive error handling

Advanced Filtering

• 📊 Summary Mode: Get package counts with 99% token reduction
• 🔎 Regex Filtering: Filter packages by pattern matching
• 📦 Category Filtering: Separate production/development dependencies (Node.js)
• 🏷️ Group Filtering: Pre-defined groups (testing, linting, building, etc.)
• 🎚️ Smart Limits: Default 50 packages to optimize LLM token usage
• 🚫 Type Exclusion: Optionally exclude @types packages

Language Support

• 📦 Node.js: Full support with dependency categorization
  • Package managers: npm, pnpm, yarn, bun
  • Production vs development classification
  • Scoped packages (@org/package)
• 🐍 Python: Full support for virtual environments
  • Package managers: pip, uv (full support), poetry, pipenv (detection)
  • Virtual environments: venv, .venv, conda
  • Bottles architecture for isolated package operations
  • Note: Dependency categorization pending

Performance Optimizations

• 💾 SQLite Cache: High-performance cache with WAL mode for concurrent access
• 📈 Relevance Scoring: Prioritizes direct dependencies (Node.js)
• 🌲 Lazy Loading: File trees loaded on-demand
• ⏱️ Fast Operations: ~150ms scan, ~10ms read, ~5ms cache hits
• 🚀 40x Faster: Validity checks in 0.03ms vs 1.2ms (old JSON cache)

Developer Experience

• 🛠️ TypeScript 5.9+: Strict mode with full type safety
• 📦 ES Modules: Modern JavaScript with import maps
• 🧪 Comprehensive Testing: 300+ tests covering all scenarios
• 🔒 Security: Path sanitization, file size limits, read-only access
• 🚀 MCP SDK: Latest Model Context Protocol implementation
• ⚙️ CI/CD: 14-stage pipeline with 4-minute total runtime

Why mcp-pkg-local?

LLMs often hallucinate APIs or use outdated syntax from their training data. This tool solves that by letting LLMs read the actual source code of packages installed in your environment, ensuring generated code matches your exact package versions.

Installation

Global Installation (Recommended)

npm install -g @descoped/mcp-pkg-local

Or use directly with npx

npx @descoped/mcp-pkg-local

MCP Client Configuration

CLI-Based Code Assistants

Claude Code (claude.ai)

Create .mcp.json in your project root:

{
  "mcpServers": {
    "pkg-local": {
      "command": "npx",
      "args": ["@descoped/mcp-pkg-local"],
      "env": {
        "DEBUG": "mcp-pkg-local:*"
      }
    }
  }
}

Or use the CLI:

claude mcp add pkg-local -- npx @descoped/mcp-pkg-local

For local development/testing with the built version:

{
  "mcpServers": {
    "pkg-local": {
      "command": "node",
      "args": ["/absolute/path/to/mcp-pkg-local/dist/index.js"],
      "env": {
        "DEBUG": "mcp-pkg-local:*"
      }
    }
  }
}

Gemini CLI

Create or edit ~/.config/gemini/mcp.json:

{
  "mcpServers": {
    "pkg-local": {
      "command": "npx",
      "args": ["@descoped/mcp-pkg-local"]
    }
  }
}

After adding, use /mcp list in Gemini CLI to verify the server is configured.

Cursor

Create .cursor/mcp.json in your project root:

{
  "mcpServers": {
    "pkg-local": {
      "command": "npx",
      "args": ["-y", "@descoped/mcp-pkg-local"],
      "cwd": "${workspaceFolder}"
    }
  }
}

Open Cursor Settings → MCP to verify connection (green status).

VS Code Extensions

Continue Extension

Add to .continue/config.json:

{
  "models": [...],
  "mcpServers": {
    "pkg-local": {
      "command": "npx",
      "args": ["@descoped/mcp-pkg-local"],
      "cwd": "${workspaceFolder}"
    }
  }
}

Windsurf

Create .windsurf/mcp.json in your project root:

{
  "mcpServers": {
    "pkg-local": {
      "command": "npx",
      "args": ["-y", "@descoped/mcp-pkg-local"]
    }
  }
}

Desktop Applications

Claude Desktop

macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "pkg-local": {
      "command": "npx",
      "args": ["-y", "@descoped/mcp-pkg-local"]
    }
  }
}

After adding, restart Claude Desktop completely. You'll see the MCP indicator (🔌) in the conversation input box.

Usage

Once configured, the MCP server provides two main tools:

Package Scanner Tools

Tool: scan-packages

Scan and index all packages in the virtual environment.

Parameters:

• forceRefresh (bool) - Force rescan even if index exists
• filter (string) - Regex pattern to filter package names (e.g., ^@types/, eslint)
• limit (number) - Max packages to return (default: 50)
• summary (bool) - Return only summary counts
• category (string) - Filter by production/development/all
• includeTypes (bool) - Include @types packages
• group (string) - Filter by group (testing, building, linting, etc.)

Examples:

// Scan with default settings (returns 50 packages)
scan-packages

// Force refresh the cache
scan-packages --forceRefresh

// Get summary only (token-efficient)
scan-packages --summary
// Returns: { total: 304, languages: { javascript: 304 }, categories: { production: 12, development: 292 } }

// Filter by regex pattern
scan-packages --filter "^react"  // All React packages
scan-packages --filter "eslint"  // Packages containing 'eslint'

// Filter by category
scan-packages --category production  // Production dependencies only
scan-packages --category development // Dev dependencies only

// Filter by predefined groups
scan-packages --group testing   // Testing tools (jest, mocha, vitest, etc.)
scan-packages --group building  // Build tools (webpack, vite, rollup, etc.)
scan-packages --group linting   // Linters (eslint, prettier, etc.)
scan-packages --group typescript // TypeScript-related packages

// Exclude @types packages
scan-packages --includeTypes false

// Limit results
scan-packages --limit 10  // Return only 10 packages

Tool: read-package

Read source files from a specific package.

Parameters:

• packageName (string, required) - Package name to read
• filePath (string) - Specific file within package
• includeTree (bool) - Include full file tree (default: false)
• maxDepth (number) - Max depth for tree traversal (default: 2)
• pattern (string) - Glob pattern to filter files (e.g., *.ts, src/**)

Examples:

// Get main files only (default - very efficient)
read-package express
// Returns: mainFiles, fileCount, package.json content

// Read specific file
read-package express lib/router/index.js

// Get full file tree
read-package express --includeTree

// Limit tree depth
read-package express --includeTree --maxDepth 2

// Filter files by pattern
read-package typescript --includeTree --pattern "*.d.ts"
read-package express --includeTree --pattern "lib/**"

Performance Features (v0.2.0)

The tool has been optimized for LLM token consumption:

Token Usage Comparison

Key Optimizations

1. Default Limits: Returns only 50 packages by default instead of all
2. Lazy File Trees: Shows only main files unless full tree is requested
3. Relative Paths: Uses relative paths to save ~30% on path strings
4. Smart Filtering: Multiple ways to get exactly what you need
5. Summary Mode: Get counts without package details
6. AST Extraction: TypeScript/JavaScript files parsed to 99.7% smaller output
7. Simplified API: Only 3 total parameters across both tools (v0.2.0)

How It Works

1. Environment Detection: Automatically detects Python (.venv/venv) or Node.js (package.json) projects
2. Package Discovery:
   • Python: Scans site-packages and reads .dist-info metadata
   • Node.js: Scans node_modules including scoped packages
3. Smart Caching: SQLite database (.pkg-local-cache/cache.db) for high-performance lookups
4. Source Reading: Provides file trees and actual source code to LLMs

Bottles Architecture

The project includes a "Bottles" architecture for isolated package management operations:

Shell-RPC Engine (BRPC-001)

• Persistent shell process management for stateful command execution
• Activity-based timeout system that resets on stdout progress
• Cross-platform support (Windows PowerShell, Linux bash, macOS bash)
• Command queueing with automatic cleanup on timeout
• Virtual environment activation support

Volume Controller (BVOL-001)

• Cache management for 12+ package managers (npm, pip, poetry, maven, etc.)
• Cross-platform cache path detection and mounting
• 10x CI/CD performance improvement through cache persistence
• Environment variable injection for consistent package operations
• Proper error handling with actionable error messages

Package Manager Adapters

• Unified interface for pip and uv (Python package managers)
• Dynamic tool detection replaces hardcoded paths
• Configurable timeouts with activity-based reset behavior
• Support for requirements.txt, pyproject.toml, and lock files
• Clean, isolated environments preventing system pollution

Development

Prerequisites

• Node.js 20+ (LTS recommended)
• npm 10+ or pnpm
• Python 3.9+ with virtual environment (for Python support)
• Node.js project with node_modules (for Node.js support)

Setup

# Clone the repository
git clone https://github.com/descoped/mcp-pkg-local.git
cd mcp-pkg-local

# Install dependencies
npm install

# Build the project
npm run build

# Run tests
npm test

# Development mode
npm run dev

# Clean build artifacts and cache
npm run clean        # Remove everything (dist, node_modules, cache)
npm run clean:cache  # Remove only cache files

Project Structure

mcp-pkg-local/
├── src/
│   ├── index.ts          # Entry point
│   ├── server.ts         # MCP server setup
│   ├── tools/            # MCP tool implementations
│   ├── scanners/         # Language-specific scanners
│   └── utils/            # Utilities
├── tests/                # Test suite
└── dist/                 # Compiled output

Testing

The project includes comprehensive tests using Vitest with configurable timeouts:

# Run all tests
npm test

# Run with coverage
npm run test:coverage

# Run in watch mode
npm run test:ui

Test Timeout Configuration

Tests use centralized timeout presets that automatically adjust for CI environments:

• Short tests (5s): Unit tests, quick validations
• Medium tests (15s): Integration tests, package operations
• Long tests (30s): End-to-end workflows, complex scenarios

In CI environments, timeouts are automatically multiplied by 1.5x for reliability.

Tests are run sequentially to avoid SQLite locking issues and race conditions.

Configuration

Environment Variables

The following environment variables can be used to customize the behavior:

Cache and Storage

• BOTTLE_CACHE_ROOT - Custom cache directory for all package data (default: .pkg-local-cache)
  • Example: export BOTTLE_CACHE_ROOT=/tmp/pkg-cache
  • Used for: Package cache, SQLite database, bottle volumes

Testing

• TEST_BASE_DIR - Base directory for test temporary files (default: output/test-temp)
• PRESERVE_TEST_DIRS_ON_FAILURE - Keep test directories on failure for debugging (default: true locally, false in CI)
• USE_SYSTEM_TEMP - Use system temp directory instead of local (default: false locally, true in CI)

Debugging

• DEBUG=mcp-pkg-local:* - Enable debug logging
• NODE_ENV=production - Production mode (disables debug features)

Timeout Configuration

• PKG_LOCAL_TIMEOUT_MULTIPLIER - Multiplier for all operation timeouts (default: 1.0)
  • Example: export PKG_LOCAL_TIMEOUT_MULTIPLIER=2 (doubles all timeouts)
  • Useful for: Slow networks, CI environments, or debugging

The system uses activity-based timeouts that reset on stdout progress:

• Quick operations (5s): Version checks, package listings
• Standard operations (30s): Package installations, virtual environment creation
• Extended operations (60s): Large installations (rarely used)

Timeouts automatically reset when commands show progress output (downloads, installations). Error output (stderr) does NOT reset timeouts to prevent hanging on failing commands.

Cache Management

The cache system uses SQLite for optimal performance:

• Location: ${BOTTLE_CACHE_ROOT}/cache.db (or .pkg-local-cache/cache.db if not set)
• Mode: WAL (Write-Ahead Logging) for concurrent access
• TTL: 1-hour default validity
• Refresh: Use --forceRefresh to force rescan

Custom Cache Location

You can customize the cache location using the BOTTLE_CACHE_ROOT environment variable:

# Absolute path
export BOTTLE_CACHE_ROOT=/tmp/pkg-cache

# Relative path (relative to project root)
export BOTTLE_CACHE_ROOT=build/cache

# In CI/CD environments
export BOTTLE_CACHE_ROOT=${CI_PROJECT_DIR}/.pkg-cache

This is particularly useful for:

• CI/CD environments where you want persistent cache between builds
• Shared development environments
• Docker containers with mounted cache volumes
• Testing with isolated cache directories

Supported Environments

Python

• ✅ Virtual environments (venv, .venv)
• ✅ Package managers: pip, poetry, uv, pipenv (basic detection)
• ✅ Standard pip packages
• ✅ Editable installations (-e)
• ✅ Namespace packages
• ⚠️ Limited: No dependency categorization yet
• 🚧 Conda environments (planned)

Node.js/JavaScript

• ✅ node_modules directory
• ✅ Package managers: npm, pnpm, yarn, bun (full support)
• ✅ Scoped packages (@org/package)
• ✅ TypeScript packages
• ✅ ESM and CommonJS modules
• ✅ Production vs development categorization

Limitations

• Python dependency categorization not yet implemented
• Local environments only (no system packages)
• Read-only access (cannot modify packages)
• 10MB file size limit for source files
• Go, Rust, Java support planned for future versions

Security

• Never reads files outside virtual environment or node_modules
• Path sanitization prevents directory traversal
• No code execution, only reading
• Binary files are blocked

Contributing

Contributions are welcome! Please read our for details.

Development Workflow

1. Fork the repository
2. Create a feature branch
3. Write tests for new features
4. Ensure all tests pass
5. Submit a pull request

Roadmap

v0.1.x (Released)

• Python virtual environment support
• Basic package scanning and reading
• MCP server implementation
• Caching system
• Performance optimizations (90% token reduction)
• Advanced filtering (regex, category, groups)
• Lazy file tree loading
• Summary mode for minimal tokens
• Node.js/JavaScript support
• Multi-package manager support

v0.2.0 (Current)

• Bottles architecture for isolated package operations
• Shell-RPC engine with activity-based timeouts
• Volume controller for cache management
• Dynamic tool detection (no hardcoded paths)
• AST extraction for TypeScript/JavaScript (99.7% reduction)
• Simplified API (77% parameter reduction)
• 300+ tests with 14 CI stages
• Production-ready error handling

Future Versions

• Python dependency categorization (critical)

• Smart package prioritization

• Conda environment support

• Package alias resolution

• Dependency tree visualization

• Go modules support

• Rust/Cargo support

• Auto-trigger on import detection

• Package documentation extraction

License

MIT License - see file for details

Acknowledgments

Built with:

• Model Context Protocol SDK
• TypeScript
• Vitest

Support

• GitHub Issues
• Documentation

Made with ❤️ for better LLM code generation