what-is-mdc.md

What are MDC Rules?

MDC rules are Markdown files (typically with a .mdc extension) that combine:

• Frontmatter: A YAML section at the top with metadata, such as a description and file patterns (globs) the rule applies to.
• Body: Markdown-formatted instructions, guidelines, or context that an AI can use to understand and interact with a codebase or dataset.

Born in the Cursor IDE’s .cursor/rules directory, MDC rules are now envisioned as a flexible, tool-agnostic standard for RAG contexts, where AI models retrieve and apply relevant information dynamically.

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Why Use MDC Rules?

• Modularity: Break instructions into small, reusable rules instead of relying on monolithic files.
• Context Awareness: Apply rules selectively based on file patterns or project areas, keeping AI responses focused.
• Portability: The Markdown format ensures compatibility with any AI tool supporting RAG.
• Scalability: Ideal for complex projects, enabling tailored instructions for different components.