AGENTS.md

OpenAI launched AGENTS.md in August 2025 and, on 9 December 2025, contributed it to the Agentic AI Foundation, a Linux Foundation directed fund co-founded with Anthropic and Block. By then more than 60,000 open source projects had adopted the format, along with agent frameworks including Cursor, Devin, GitHub Copilot, Gemini CLI and VS Code. What is being governed is a Markdown file carrying project-specific instructions: code conventions, build steps, test requirements.

Jude Gao at Vercel measured what that file buys. Next.js 16 APIs absent from model training data produced incorrect code in 47% of cases. skills packaging the same knowledge went uninvoked in 56% of eval runs, leaving the success rate at the 53% baseline, and reached only 79% once instructions forced the trigger. A static AGENTS.md injected into the system prompt at every turn scored 100% on build, lint and tests. Vercel then compressed 40 KB of documentation into an 8 KB pipe-delimited index without losing that score, because passive context consumes window on every interaction.

Addy Osmani frames the file as a rationing problem. Under the ratchet principle, each line must trace to a concrete past failure; HumanLayer's ceiling is under 60 lines, a pilot's checklist rather than a style guide.

Bill Staples of GitLab distinguishes the Markdown file from the governable record. Context, identity, policy, provenance and organizational memory have to persist across models and agents, which for him points toward a control plane rather than a file in the repository.