Rules files by tool
The advice can be the same. The filename cannot. Each page shows the format that tool loads today and a sample file.
Cursor
.cursor/rules/project.mdcHow Cursor project rules work in 2026: .cursor/rules/*.mdc frontmatter, alwaysApply, and the legacy .cursorrules file.
Claude Code
CLAUDE.mdWhere Claude Code reads CLAUDE.md and how .claude/rules path-scoped rules work.
Windsurf
.devin/rules/project.mdWindsurf and Devin Desktop rules: .devin/rules, the .windsurf/rules fallback, and legacy .windsurfrules.
GitHub Copilot
.github/copilot-instructions.mdGitHub Copilot custom instructions: .github/copilot-instructions.md and path-specific .instructions.md files.
Codex
AGENTS.mdHow OpenAI Codex discovers AGENTS.md, nested files, and the AGENTS.override.md footgun.
AGENTS.md
AGENTS.mdWhat the AGENTS.md standard is, which coding agents read it, and how nested files work.