the three-layer agent context stack
AGENTS.md (project level, session start)
adopted by 60k+ repos as of April 2026
/repo-root/AGENTS.md
# Project: my-service
## Conventions: TypeScript, pnpm, Pydantic models, RFC 2119 MUST
## Commands: pnpm dev, pnpm build, pnpm test
SKILL.md (reusable know-how, loaded on invoke)
Anthropic Agent Skills, open standard, December 2025
/skills/release-notes-writer/SKILL.md
---
name: release-notes-writer
description: Write a changelog entry for the latest PRs.
---
MCP server (tools the skill invokes)
Phase 13 / 06-14 covers the protocol
notes-server + github-server + gateway
MCP = "what tools exist"; Skill = "how to use them"; AGENTS.md = "project rules"
Apps SDK (OpenAI) is MCP + widget metadata for ChatGPT UI.