What is Rules (Claude Code Rules)?
Markdown files in .claude/rules/ that define specific behavioral constraints for Claude.
Detailed Explanation
Rules are markdown files stored in the .claude/rules/ directory that define specific behavioral constraints and guidelines for Claude Code. Unlike CLAUDE.md (which is always active), rules can have conditional activation based on file patterns via frontmatter. They are ideal for language-specific conventions, framework guidelines, and context-specific instructions that should only apply when working with certain file types or in certain directories.