Repository Rules in Codegen act as a persistent set of instructions or a “system prompt” for the AI agent whenever it operates on a specific repository. These rules guide the agent’s behavior by enforcing coding standards and repository-specific conventions through automated reminders to the language model (LLM) during each task.

Codegen supports two types of repository rules:

  1. Manual Repository Rules - configured through the web interface
  2. Automatic Rule File Detection - automatically discovered from your repository files

Update repo rules at codegen.com/repos

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How Repository Rules Work

When an agent is assigned a task on a repository with defined rules, those rules are automatically prepended or made available to the LLM as part of its context. This means the agent “sees” these rules alongside the actual task or prompt it receives.

For example, if you have a rule like “Always use tabs for indentation,” the agent will be reminded of this preference before it starts writing or modifying code in that repository.

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Accessing and Configuring Repository Rules

You can typically find and configure Repository Rules within the settings page for each specific repository in the Codegen web UI.

  1. Navigate to codegen.com/repos.
  2. Select the repository for which you want to set rules.
  3. Look for a section titled “Repository rules” or similar in the repository’s settings.

Update repo rules at codegen.com/repos

In the text area provided (as shown in the image), you can specify any rules you want the agent to follow for this repository. Click “Save” to apply them.

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Automatic Rule File Detection

In addition to manual repository rules, Codegen automatically discovers and includes agent rule files from your repository when the agent starts working on it. This happens automatically whenever the set_active_codebase tool is used.

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Supported Rule File Patterns

Codegen automatically searches for the following types of rule files in your repository:

  • .cursorrules - Cursor AI editor rules
  • .clinerules - Cline AI assistant rules
  • .windsurfrules - Windsurf AI editor rules
  • **/*.mdc - Markdown files with .mdc extension anywhere in the repository
  • .cursor/rules/**/*.mdc - Markdown files in the .cursor/rules/ directory structure

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How Automatic Detection Works

  1. File Discovery: When you switch to a repository, Codegen uses ripgrep to search for files matching the supported patterns
  2. Content Extraction: The content of discovered files is read and processed
  3. Size Limitation: All rule files combined are truncated to fit within 3,000 characters total to ensure optimal performance
  4. Context Integration: The rule content is automatically included in the agent’s context alongside any manual repository rules

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Example Rule Files

Here are examples of how you might structure automatic rule files in your repository:

.cursorrules example:

Use TypeScript for all new code
Follow the existing code style in the repository
Always add JSDoc comments for public functions
Prefer functional components over class components in React

.cursor/rules/backend.mdc example:

# Backend Development Rules

## Database
- Use Prisma for database operations
- Always use transactions for multi-step operations
- Include proper error handling for all database calls

## API Design
- Follow REST conventions
- Use proper HTTP status codes
- Include request/response validation

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Benefits of Automatic Rule Files

  • Version Control: Rule files are committed with your code, ensuring consistency across team members
  • Repository-Specific: Different repositories can have different rule files without manual configuration
  • Developer-Friendly: Developers can manage rules using familiar file-based workflows
  • Editor Integration: Many AI-powered editors already support these file formats

Automatic rule files work alongside manual repository rules. Both types of rules are combined and provided to the agent for maximum context.

If your rule files exceed 3,000 characters combined, they will be automatically truncated. Consider keeping rule files concise or splitting them into multiple focused files.

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Common Use Cases and Examples

Repository rules are flexible and can be used for various purposes:

  • Enforcing Linting/Formatting:
    • “Remember to run the linter with npm run lint before committing.”
    • “Ensure all Python code follows PEP 8 guidelines. Use black for formatting.”
  • Specifying Commit Message Conventions:
    • “All commit messages must follow the Conventional Commits specification.”
    • “Prefix commit messages with the related Linear issue ID (e.g., ENG-123: ...).”
  • Highlighting Project-Specific Information:
    • “This repository uses TypeScript. All new backend code should be in the /server/src directory.”
    • “Avoid using deprecated function old_function(). Use new_function() instead.”
  • Code Style Preferences:
    • “Don’t write super long strings, as this will break pre-commit. Do triple-quoted strings with newlines, non-indented, instead!” (As seen in your example image)
    • “Prefer functional components over class components in React.”
  • Reminders for Testing:
    • “Ensure all new features have corresponding unit tests.”
    • “Run integration tests with npm run test:integration after significant changes.”

Keep your repository rules concise and clear. Overly complex or numerous rules might confuse the agent or lead to suboptimal performance. Focus on the most critical guidelines for each repository.

Both manual repository rules and automatic rule files are applied in addition to any global prompting strategies or agent capabilities. They provide a repository-specific layer of instruction that helps ensure consistent behavior across your codebase.