Claude Code configs: CLAUDE.md vs .claude/rules/ for AI coding

Claude Code supports project-level CLAUDE.md files for global context and modular .claude/rules/ files for path-scoped instructions. The article explains when to use each, recommending CLAUDE.md for commands and core architecture, and .claude/rules/ for domain-specific rules to optimize token usage. Best practices include keeping CLAUDE.md under 150 lines and using sub-directory CLAUDE.md files in monorepos.