Teams, individuals, and open-source projects often rely on multiple AI coding agents working in the same project. Valuable rules, encoding norms and conventions, documentation, and helpful hints for the AI, are maintained in separate locations and formats for each agent.

Ruler makes it easy to manage the rules for all agents centrally, and distributing them to their agent-specific location as needed.

Ruler: Centralise Your AI Coding Assistant Instructions

• GitHub: intellectronica/ruler
• NPM: @intellectronica/ruler

Beta Research Preview

• Please test this version carefully in your environment
• Report issues at https://github.com/intellectronica/ruler/issues

Why Ruler?

Managing instructions across multiple AI coding tools becomes complex as your team grows. Different agents (GitHub Copilot, Claude, Cursor, Aider, etc.) require their own configuration files, leading to:

• Inconsistent guidance across AI tools
• Duplicated effort maintaining multiple config files
• Context drift as project requirements evolve
• Onboarding friction for new AI tools

Ruler solves this by providing a single source of truth for all your AI agent instructions, automatically distributing them to the right configuration files.

Core Features

• Centralised Rule Management: Store all AI instructions in a dedicated .ruler/ directory using Markdown files
• Automatic Distribution: Ruler applies these rules to configuration files of supported AI agents
• Targeted Agent Configuration: Fine-tune which agents are affected and their specific output paths via ruler.toml
• MCP Server Propagation: Manage and distribute Model Context Protocol (MCP) server settings
• .gitignore Automation: Keeps generated agent config files out of version control automatically
• Simple CLI: Easy-to-use commands for initialising and applying configurations

Supported AI Agents

Getting Started

Prerequisites

Node.js 18.x or higher is required.

Installation

Global Installation (Recommended for CLI use):

npm install -g @intellectronica/ruler

Using npx (for one-off commands):

npx @intellectronica/ruler apply

Project Initialisation

1. Navigate to your project’s root directory
2. Run ruler init
3. This creates:
   • .ruler/ directory
   • .ruler/instructions.md: A starter Markdown file for your rules
   • .ruler/ruler.toml: The main configuration file for Ruler
   • .ruler/mcp.json: An example MCP server configuration

Core Concepts

The .ruler/ Directory

This is your central hub for all AI agent instructions:

• Rule Files (*.md): Discovered recursively from .ruler/ and alphabetically concatenated
• Concatenation Marker: Each file’s content is prepended with --- Source: <relative_path_to_md_file> --- for traceability
• ruler.toml: Master configuration for Ruler’s behavior, agent selection, and output paths
• mcp.json: Shared MCP server settings

Best Practices for Rule Files

Granularity: Break down complex instructions into focused .md files:

• coding_style.md
• api_conventions.md
• project_architecture.md
• security_guidelines.md

Example rule file (.ruler/python_guidelines.md):

# Python Project Guidelines

## General Style
- Follow PEP 8 for all Python code
- Use type hints for all function signatures and complex variables
- Keep functions short and focused on a single task

## Error Handling
- Use specific exception types rather than generic `Exception`
- Log errors effectively with context

## Security
- Always validate and sanitize user input
- Be mindful of potential injection vulnerabilities

Usage: The apply Command

Primary Command

ruler apply [options]

Options

Common Examples

Apply rules to all configured agents:

ruler apply

Apply rules only to GitHub Copilot and Claude:

ruler apply --agents copilot,claude

Use a specific configuration file:

ruler apply --config ./team-configs/ruler.frontend.toml

Apply rules with verbose output:

ruler apply --verbose

Apply rules but skip MCP and .gitignore updates:

ruler apply --no-mcp --no-gitignore

Configuration (ruler.toml) in Detail

Location

Defaults to .ruler/ruler.toml in the project root. Override with --config CLI option.

Complete Example

# Default agents to run when --agents is not specified
# Uses case-insensitive substring matching
default_agents = ["copilot", "claude", "aider"]

# --- Global MCP Server Configuration ---
[mcp]
# Enable/disable MCP propagation globally (default: true)
enabled = true
# Global merge strategy: 'merge' or 'overwrite' (default: 'merge')
merge_strategy = "merge"

# --- Global .gitignore Configuration ---
[gitignore]
# Enable/disable automatic .gitignore updates (default: true)
enabled = true

# --- Agent-Specific Configurations ---
[agents.copilot]
enabled = true
output_path = ".github/copilot-instructions.md"

[agents.claude]
enabled = true
output_path = "CLAUDE.md"

[agents.aider]
enabled = true
output_path_instructions = "ruler_aider_instructions.md"
output_path_config = ".aider.conf.yml"

# Agent-specific MCP configuration
[agents.cursor.mcp]
enabled = true
merge_strategy = "merge"

# Disable specific agents
[agents.windsurf]
enabled = false

Configuration Precedence

1. CLI flags (e.g., --agents, --no-mcp, --mcp-overwrite, --no-gitignore)
2. Settings in ruler.toml (default_agents, specific agent settings, global sections)
3. Ruler’s built-in defaults (all agents enabled, standard output paths, MCP enabled with ‘merge’)

MCP (Model Context Protocol) Server Configuration

MCP provides broader context to AI models through server configurations. Ruler can manage and distribute these settings across compatible agents.

.ruler/mcp.json

Define your project’s MCP servers:

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/project"]
    },
    "git": {
      "command": "npx", 
      "args": ["-y", "@modelcontextprotocol/server-git", "--repository", "."]
    }
  }
}

Ruler uses this file with the merge (default) or overwrite strategy, controlled by ruler.toml or CLI flags.

.gitignore Integration

Ruler automatically manages your .gitignore file to keep generated agent configuration files out of version control.

How it Works

• Creates or updates .gitignore in your project root
• Adds paths to a managed block marked with # START Ruler Generated Files and # END Ruler Generated Files
• Preserves existing content outside this block
• Sorts paths alphabetically and uses relative POSIX-style paths

Example .gitignore Section

# Your existing rules
node_modules/
*.log

# START Ruler Generated Files
.aider.conf.yml
.clinerules
.cursor/rules/ruler_cursor_instructions.md
.github/copilot-instructions.md
.windsurf/rules/ruler_windsurf_instructions.md
AGENTS.md
CLAUDE.md
ruler_aider_instructions.md
# END Ruler Generated Files

dist/

Control Options

• CLI flags: --gitignore or --no-gitignore
• Configuration: [gitignore].enabled in ruler.toml
• Default: enabled

Practical Usage Scenarios

Scenario 1: Getting Started Quickly

# Initialize Ruler in your project
cd your-project
ruler init

# Edit the generated files
# - Add your coding guidelines to .ruler/instructions.md
# - Customize .ruler/ruler.toml if needed

# Apply rules to all AI agents
ruler apply

Scenario 2: Team Standardization

1. Create .ruler/coding_standards.md, .ruler/api_usage.md
2. Commit the .ruler directory to your repository
3. Team members pull changes and run ruler apply to update their local AI agent configurations

Scenario 3: Project-Specific Context for AI

1. Detail your project’s architecture in .ruler/project_overview.md
2. Describe primary data structures in .ruler/data_models.md
3. Run ruler apply to help AI tools provide more relevant suggestions

Integration with NPM Scripts

{
  "scripts": {
    "ruler:apply": "ruler apply",
    "dev": "npm run ruler:apply && your_dev_command",
    "precommit": "npm run ruler:apply"
  }
}

Integration with GitHub Actions

# .github/workflows/ruler-check.yml
name: Check Ruler Configuration
on:
  pull_request:
    paths: ['.ruler/**']

jobs:
  check-ruler:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '18'
          cache: 'npm'
      
      - name: Install Ruler
        run: npm install -g @intellectronica/ruler
      
      - name: Apply Ruler configuration
        run: ruler apply --no-gitignore
      
      - name: Check for uncommitted changes
        run: |
          if [[ -n $(git status --porcelain) ]]; then
            echo "::error::Ruler configuration is out of sync!"
            echo "Please run 'ruler apply' locally and commit the changes."
            exit 1
          fi

Troubleshooting

Common Issues

“Cannot find module” errors:

• Ensure Ruler is installed globally: npm install -g @intellectronica/ruler
• Or use npx @intellectronica/ruler

Permission denied errors:

• On Unix systems, you may need sudo for global installation

Agent files not updating:

• Check if the agent is enabled in ruler.toml
• Verify agent isn’t excluded by --agents flag
• Use --verbose to see detailed execution logs

Configuration validation errors:

• Ruler now validates ruler.toml format and will show specific error details
• Check that all configuration values match the expected types and formats

Debug Mode

Use --verbose flag to see detailed execution logs:

ruler apply --verbose

This shows:

• Configuration loading details
• Agent selection logic
• File processing information
• MCP configuration steps

FAQ

Q: Can I use different rules for different agents? A: Currently, all agents receive the same concatenated rules. For agent-specific instructions, include sections in your rule files like ”## GitHub Copilot Specific” or ”## Aider Configuration”.

Q: How do I temporarily disable Ruler for an agent? A: Set enabled = false in ruler.toml under [agents.agentname], or use --agents flag to specify only the agents you want.

Q: What happens to my existing agent configuration files? A: Ruler creates backups with .bak extension before overwriting any existing files.

Q: Can I run Ruler in CI/CD pipelines? A: Yes! Use ruler apply --no-gitignore in CI to avoid modifying .gitignore. See the GitHub Actions example above.

Q: How do I migrate from version 0.1.x to 0.2.0? A: Version 0.2.0 is backward compatible. Your existing .ruler/ directory and ruler.toml will continue to work. New features like verbose logging and improved error messages are opt-in.

Development

Setup

git clone https://github.com/intellectronica/ruler.git
cd ruler
npm install
npm run build

Testing

# Run all tests
npm test

# Run tests with coverage
npm run test:coverage

# Run tests in watch mode
npm run test:watch

Code Quality

# Run linting
npm run lint

# Run formatting
npm run format

Contributing

Contributions are welcome! Please:

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests for new functionality
5. Ensure all tests pass
6. Submit a pull request

For bugs and feature requests, please open an issue.

License

MIT

© Eleanor Berger
ai.intellectronica.net