Ruler: Centralise Your AI Coding Assistant Instructions

GitHub: intellectronica/ruler NPM: @intellectronica/ruler Animation by Isaac Flath of Elite AI-Assisted Coding ➡︎

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
• Complex project structures requiring context-specific instructions for different components

Ruler solves this by providing a single source of truth for all your AI agent instructions, automatically distributing them to the right configuration files. With support for nested rule loading, Ruler can handle complex project structures with context-specific instructions for different components.

Core Features

• Centralised Rule Management: Store all AI instructions in a dedicated .ruler/ directory using Markdown files
• Nested Rule Loading: Support complex project structures with multiple .ruler/ directories for context-specific instructions
• 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

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/AGENTS.md: The primary starter Markdown file for your rules
• .ruler/ruler.toml: The main configuration file for Ruler (now contains sample MCP server sections; legacy .ruler/mcp.json no longer scaffolded)
• (Optional legacy fallback) If you previously used .ruler/instructions.md, it is still respected when AGENTS.md is absent. (The prior runtime warning was removed.)

Additionally, you can create a global configuration to use when no local .ruler/ directory is found:

ruler init --global

The global configuration will be created to $XDG_CONFIG_HOME/ruler (default: ~/.config/ruler).

Core Concepts

The .ruler/ Directory

This is your central hub for all AI agent instructions:

• Primary File Order & Precedence:
  1. A repository root AGENTS.md (outside .ruler/) if present (highest precedence, prepended)
  2. .ruler/AGENTS.md (new default starter file)
  3. Legacy .ruler/instructions.md (only if .ruler/AGENTS.md absent; no longer emits a deprecation warning)
  4. Remaining discovered .md files under .ruler/ (and subdirectories) in sorted order
• Rule Files (*.md): Discovered recursively from .ruler/ or $XDG_CONFIG_HOME/ruler and concatenated in the order above
• 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

This ordering lets you keep a short, high-impact root AGENTS.md (e.g. executive project summary) while housing detailed guidance inside .ruler/.

Nested Rule Loading

Ruler now supports nested rule loading with the --nested flag, enabling context-specific instructions for different parts of your project:

project/
├── .ruler/           # Global project rules
│   ├── AGENTS.md
│   └── coding_style.md
├── src/
│   └── .ruler/       # Component-specific rules
│       └── api_guidelines.md
├── tests/
│   └── .ruler/       # Test-specific rules
│       └── testing_conventions.md
└── docs/
    └── .ruler/       # Documentation rules
        └── writing_style.md

How it works:

• Discover all .ruler/ directories in the project hierarchy
• Load and concatenate rules from each directory in order
• Enable with: ruler apply --nested

Perfect for:

• Monorepos with multiple services
• Projects with distinct components (frontend/backend)
• Teams needing different instructions for different areas
• Complex codebases with varying standards

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]

The apply command looks for .ruler/ in the current directory tree, reading the first match. If no such directory is found, it will look for a global configuration in $XDG_CONFIG_HOME/ruler.

Options

Common Examples

Apply rules to all configured agents:

ruler apply

Apply rules only to GitHub Copilot and Claude:

ruler apply --agents copilot,claude

Apply rules only to Firebase Studio:

ruler apply --agents firebase

Apply rules only to Warp:

ruler apply --agents warp

Apply rules only to Trae AI:

ruler apply --agents trae

Apply rules only to RooCode:

ruler apply --agents roo

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

Usage: The revert Command

The revert command safely undoes all changes made by ruler apply, restoring your project to its pre-ruler state. It intelligently restores files from backups (.bak files) when available, or removes generated files that didn't exist before.

Why Revert is Needed

When experimenting with different rule configurations or switching between projects, you may want to:

• Clean slate: Remove all ruler-generated files to start fresh
• Restore originals: Revert modified files back to their original state
• Selective cleanup: Remove configurations for specific agents only
• Safe experimentation: Try ruler without fear of permanent changes

Primary Command

ruler revert [options]

Options

Common Examples

Revert all ruler changes:

ruler revert

Preview what would be reverted (dry-run):

ruler revert --dry-run

Revert only specific agents:

ruler revert --agents claude,copilot

Revert with detailed output:

ruler revert --verbose

Keep backup files after reverting:

ruler revert --keep-backups

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"

# --- MCP Server Definitions ---
[mcp_servers.filesystem]
command = "npx"
args = ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/project"]

[mcp_servers.git]
command = "npx"
args = ["-y", "@modelcontextprotocol/server-git", "--repository", "."]

[mcp_servers.remote_api]
url = "https://api.example.com"

[mcp_servers.remote_api.headers]
Authorization = "Bearer your-token"

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

# --- Agent-Specific Configurations ---
[agents.copilot]
enabled = true

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

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

# OpenAI Codex CLI agent and MCP config
[agents.codex]
enabled = true
output_path = "AGENTS.md"
output_path_config = ".codex/config.toml"

# Agent-specific MCP configuration for Codex CLI
[agents.codex.mcp]
enabled = true
merge_strategy = "merge"

[agents.firebase]
enabled = true
output_path = ".idx/airules.md"

[agents.gemini-cli]
enabled = true

[agents.jules]
enabled = true

[agents.junie]
enabled = true
output_path = ".junie/guidelines.md"

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

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

[agents.kilocode]
enabled = true
output_path = ".kilocode/rules/ruler_kilocode_instructions.md"

[agents.warp]
enabled = true
output_path = "WARP.md"

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.

TOML Configuration (Recommended)

You can now define MCP servers directly in ruler.toml using the [mcp_servers.<name>] syntax:

# Global MCP behavior
[mcp]
enabled = true
merge_strategy = "merge"  # or "overwrite"

# Local (stdio) server
[mcp_servers.filesystem]
command = "npx"
args = ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/project"]

[mcp_servers.filesystem.env]
API_KEY = "your-api-key"

# Remote server
[mcp_servers.search]
url = "https://mcp.example.com"

[mcp_servers.search.headers]
Authorization = "Bearer your-token"
"X-API-Version" = "v1"

Legacy .ruler/mcp.json (Deprecated)

For backward compatibility, you can still use the JSON format; a warning is issued encouraging migration to TOML. The file is no longer created during ruler init.

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

Configuration Precedence

When both TOML and JSON configurations are present:

1. TOML servers take precedence over JSON servers with the same name
2. Servers are merged from both sources (unless using overwrite strategy)
3. Deprecation warning is shown encouraging migration to TOML (warning shown once per run)

Server Types

Local/stdio servers require a command field:

[mcp_servers.local_server]
command = "node"
args = ["server.js"]

[mcp_servers.local_server.env]
DEBUG = "1"

Remote servers require a url field (headers optional; bearer Authorization token auto-extracted for OpenHands when possible):

[mcp_servers.remote_server]
url = "https://api.example.com"

[mcp_servers.remote_server.headers]
Authorization = "Bearer token"

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

Home Directory Safety: Ruler never writes MCP configuration files outside your project root. Any historical references to user home directories (e.g. ~/.codeium/windsurf/mcp_config.json or ~/.zed/settings.json) have been removed; only project-local paths are targeted.

Note for OpenAI Codex CLI: To apply the local Codex CLI MCP configuration, set the CODEX_HOME environment variable to your project’s .codex directory:

export CODEX_HOME="$(pwd)/.codex"

.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 (sample - actual list depends on enabled agents)

# Your existing rules
node_modules/
*.log

# START Ruler Generated Files
.aider.conf.yml
.clinerules
.cursor/rules/ruler_cursor_instructions.mdc
.windsurf/rules/ruler_windsurf_instructions.md
AGENTS.md
CLAUDE.md
AGENTS.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/AGENTS.md (or keep adding additional .md files)
# - Customize .ruler/ruler.toml if needed

# Apply rules to all AI agents
ruler apply

Scenario 2: Complex Projects with Nested Rules

For large projects with multiple components or services, use nested rule loading:

# Set up nested .ruler directories
mkdir -p src/.ruler tests/.ruler docs/.ruler

# Add component-specific instructions
echo "# API Design Guidelines" > src/.ruler/api_rules.md
echo "# Testing Best Practices" > tests/.ruler/test_rules.md
echo "# Documentation Standards" > docs/.ruler/docs_rules.md

# Apply with nested loading
ruler apply --nested --verbose

This creates context-specific instructions for different parts of your project while maintaining global rules in the root .ruler/ directory.

Scenario 3: 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 4: 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 set up different instructions for different parts of my project? A: Use the --nested flag with ruler apply --nested. This enables Ruler to discover and load rules from multiple .ruler/ directories throughout your project hierarchy. Place component-specific instructions in src/.ruler/, test-specific rules in tests/.ruler/, etc., while keeping global rules in the root .ruler/ directory.

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 older versions using instructions.md? A: Simply rename .ruler/instructions.md to .ruler/AGENTS.md (recommended). If you keep the legacy file and omit AGENTS.md, Ruler will still use it (without emitting the old deprecation warning). Having both causes AGENTS.md to take precedence; the legacy file is still concatenated afterward.

Q: How does OpenHands MCP propagation classify servers? A: Local stdio servers become stdio_servers. Remote URLs containing /sse are classified as sse_servers; others become shttp_servers. Bearer tokens in an Authorization header are extracted into api_key where possible.

Q: Where is Zed configuration written now? A: Ruler writes a settings.json in the project root (not the user home dir) and transforms MCP server definitions to Zed's context_servers format including source: "custom".

Q: What changed about MCP initialization? A: ruler init now only adds example MCP server sections to ruler.toml instead of creating .ruler/mcp.json. The JSON file is still consumed if present, but TOML servers win on name conflicts.

Q: Is Kiro supported? A: Yes. Kiro receives concatenated rules at .kiro/steering/ruler_kiro_instructions.md.

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