Introduction

Lien (French for "link" or "connection") is a local-first code-intelligence layer for AI coding assistants like Cursor and Claude Code, delivered through the Model Context Protocol (MCP).

What is Lien?

Lien indexes your codebase locally and gives AI assistants the structural context they need to work safely: reverse dependencies and blast radius, complexity hotspots, and test associations — plus fast lexical code search for discovery. Unlike cloud-based solutions, everything runs on your machine—your code never leaves your computer.

Setup takes 30 seconds: Install globally, run lien init, restart your AI assistant. There's no model to download — the first index runs instantly and offline.

Key Benefits

Zero Configuration

Lien auto-detects your project structure and "just works." No config files, no framework selection, no pattern configuration.

Privacy First

Your code is precious intellectual property. Lien processes everything locally with no external API calls, no data collection, and no telemetry.

Structural Intelligence

The questions an agent needs answered before editing your code — "what depends on this?", "how complex is this?", "what tests cover it?" — are answered from an accurate import graph and per-symbol metrics, not guessed.

Explainable Lexical Search

For discovery, Lien runs full-text (FTS5/BM25) keyword search over code, docstrings, and identifier-split symbol names. It's keyword-based, not meaning-based — query with terms that appear in the code, and you can always see why a result matched.

AI-Powered Development

Integrate with Cursor, Claude Code, and other MCP-compatible tools to give AI assistants deep context about your codebase, enabling better suggestions and answers.

Framework Aware

Automatically detects and adapts to your project structure:

• Node.js/TypeScript: Package.json detection, Jest/Vitest/Mocha support
• Laravel/PHP: Composer detection, blade templates, frontend assets
• Monorepo: Multiple frameworks in one repository

Additionally, 15+ languages (including Liquid, Go, Rust, Python, and more) are indexed out of the box via the default scan pattern.

How Does It Work?

1. Scan: Lien walks your codebase and identifies source files based on ecosystem detection
2. Chunk: Files are split into semantic chunks (functions, classes, logical blocks) via Tree-sitter AST parsing
3. Enrich: Each chunk gets complexity metrics, imports/exports, call sites, and test associations
4. Store: Chunks and the import graph are written to a local SQLite database — no embeddings, no model
5. Answer: Structural queries (dependents, complexity, context) are served with indexed SQL; discovery is served with FTS5/BM25 keyword search
6. Retrieve: Relevant chunks and structural facts are returned with context

Use Cases

Understanding New Codebases

Quickly understand how a new codebase works without reading every file:

• "Show me the database schema"
• "How is error handling implemented?"
• "Where are API routes defined?"

Finding Implementations

Locate specific functionality across a large codebase:

• "Find JWT token validation"
• "Show authentication middleware"
• "Where is user registration handled?"

Discovering Patterns

Find similar code patterns for refactoring or consistency:

• "Find similar validation functions"
• "Show all database queries"
• "Locate API endpoint handlers"

Test Coverage

Understand what tests cover specific code:

• "What tests cover this module?"
• "Show related test files"
• "Find test patterns for this feature"

Architecture

Lien is built with modern, performant tools:

• TypeScript for type-safe development
• Tree-sitter for AST-based chunking and complexity analysis
• SQLite (better-sqlite3) for the structural store, with FTS5/BM25 for lexical search
• MCP SDK for AI assistant integration
• Commander.js for CLI

Supported Languages

Full AST Support (function detection, complexity analysis):

• TypeScript, JavaScript (JSX/TSX)
• Python
• PHP
• Rust
• Go
• Java
• C#
• Ruby
• Kotlin
• Swift

Indexed for lexical search (chunking + FTS5):

• All of the above, plus Vue, Liquid, C/C++, Scala, Markdown

Next Steps

Ready to get started? Follow our installation guide to set up Lien in minutes.