Lex

UK legal API for AI agents and researchers. Access comprehensive UK legislation data with semantic search and Model Context Protocol integration.

What is Lex?

Lex provides programmatic access to 8.4M+ UK legal documents - legislation, amendments, and explanatory notes - with hybrid semantic search.

This is an experimental service and should not be used as a production dependency.

Dataset Coverage

• Legislation - 220K Acts and Statutory Instruments (1267-present, complete from 1963)
• Amendments - 892K legislative changes and modifications
• Explanatory Notes - 89K notes providing legislative context
• Case Law - 70K judgments and 4.7M paragraphs (temporarily disabled pending TNA licence)
• PDF Digitisation - Historical legislation (pre-1963) digitised using AI

What Can You Build?

• Legal Research - Find relevant legislation in seconds
• Policy Analysis - Track legislative changes over time
• AI Grounding - Ground AI assistants in authoritative UK legal sources

MCP Integration

Connect AI assistants to Lex via Model Context Protocol. See the live documentation for setup instructions for:

• Claude Desktop
• Claude Code
• Cursor
• Microsoft Copilot Studio
• VS Code + GitHub Copilot

Local Development

Prerequisites

• Python 3.12+
• uv
• Docker & Docker Compose
• Azure OpenAI credentials

Quick Start

# Clone and setup
git clone https://github.com/i-dot-ai/lex.git && cd lex
cp .env.example .env  # Add your Azure OpenAI keys

# Start services and load sample data
docker compose up -d
make ingest-all-sample

# Visit http://localhost:8000/docs for API documentation

Data Loading

# Quick samples (recommended for testing)
make ingest-legislation-sample
make ingest-all-sample

# Full datasets (production use)
make ingest-legislation-full
make ingest-all-full

# Create indexes for fast filtering
uv run python scripts/create_payload_indexes.py

Development Commands

make install          # Install dependencies
make test             # Run tests
make run              # Start API locally (without Docker)
uv run ruff format .  # Format code

Architecture

lex/
├── src/
│   ├── lex/              # Data pipeline (scraping, parsing, indexing)
│   └── backend/          # API server (FastAPI + MCP)
├── infrastructure/       # Azure Bicep templates and deploy scripts
├── scripts/              # Maintenance, migration, and export utilities
├── tests/                # Test suite
└── docs/                 # Documentation

Documentation

• System Architecture - Start here for the full picture
• Deployment Guide
• Operations Runbook
• Data Pipeline Guide
• API Reference
• Troubleshooting
• Contributing

Acknowledgements

Built with support from The National Archives and Ministry of Justice.

License

MIT - See LICENSE for details.