Four Instruction Files: CLAUDE.md, AGENTS.md, and More
Day 8 · Week 2 · Context — The Secret Sauce
Slack Message — copy & paste
🤖 Tip #8 — Four instruction files exist across platforms. Know who reads what — and use the env var trick to share rules without duplication.
#8 All Tools
Who Reads What
- **CLAUDE.md** — Claude Code's primary file. Also read by Copilot coding agent (the cloud autonomous agent that works on GitHub issues). Supports @import for recursive includes.
- **AGENTS.md** — the new open format (Aug 2025). Read by Copilot CLI, VS Code Chat, and the coding agent. Placed at root or nested per-directory.
- **.github/copilot-instructions.md** — the original Copilot format. Still works. Repo-wide scope.
- **.github/instructions/*.instructions.md** — path-scoped with `applyTo:` frontmatter. Like .claude/rules/ but for Copilot. Can exclude specific agents with `excludeAgent:`.
CLAUDE.md AGENTS.md copilot-instructions Instructions
#8 Context — The Secret Sauce
Cross-Platform Sharing
- 1 The sharing trick — no duplication needed
- › Set `COPILOT_CUSTOM_INSTRUCTIONS_DIRS=".claude/rules"` as an env var
- › Now BOTH Claude Code and Copilot CLI read the same rules
- › Still need dual frontmatter (`paths:` + `applyTo:`) for path-matching in both tools
- 2 Check which instruction files your project has — ensure each tool can find what it needs
- 3 Set `COPILOT_CUSTOM_INSTRUCTIONS_DIRS=".claude/rules"` so Copilot CLI reads your existing Claude Code rules
- 4 Use dual frontmatter (`paths:` for Claude Code + `applyTo:` for Copilot) in all rule files for cross-platform path-matching
CLAUDE.md AGENTS.md copilot-instructions Instructions
Your screenshot here Optional — add a screenshot from your own workflow