L4 Tutorials

Task-oriented guides to help you accomplish specific goals with L4. Each tutorial is self-contained and focused on a particular use case or audience.

Getting Started

New to L4? Start here:

Your First L4 File - Create and run a simple L4 program
Using the l4 CLI - Install and use the l4 command-line tool
Testing Your Rules - Write tests for your L4 rules
Debugging Type Errors - Understand and fix the type checker's error messages
Version Control for Rules - Manage L4 files with git
Encoding Legislation - Turn legal text into L4
Wedding Vows - Fun intro to regulative rules

See also: Common Patterns - a quick reference of frequently used L4 patterns.

Write functions that read like legal prose:

Infix, Postfix, and Mixfix Functions - Call functions in natural word order
Optimising for Natural Language Document Generation with @nlg - Make the rendered prose read as naturally as possible, then refine it with Legalese AI

Prerequisites: Basic function syntax

Export your L4 rules as live REST API endpoints:

Exporting Rules for Deployment - Mark rules with @export, deploy from VS Code, and call them via REST or WebMCP
OpenAI- and Anthropic-Compatible AI APIs - Chat with a deployment's rules from any OpenAI or Anthropic client (legalese-comply-4)
MCP Server - Expose deployed rules as Model Context Protocol tools
Using Your Rules from Claude - Connect Claude to your deployed rules
Install a Deployment as an AI Agent Plugin - Bundle a deployment's SKILL.md + MCP server into an agent plugin
Use Deployed Rules from an AI Agent (MCP) - Connect an agent to the org's rules MCP server; it finds and calls the right rule (scales to many deployments)
WebMCP Embed Script - One embed tag so your website serves its own rules
RESTful OpenAPI Specification - Generate clients and call rules as plain REST

Prerequisites: Basic L4 knowledge

Working with AI and language models in L4:

Prerequisites: Basic L4 knowledge