What Is AGENTS.md? How to Write One in 2026

AGENTS.md is an open Markdown format designed to provide AI coding agents with essential context and instructions for working on a project, functioning as a "README for agents." It has become a widely adopted standard among over 60,000 open-source projects, enabling agents to understand build commands, test instructions, and conventions without cluttering the human-centric README files. This format is vendor-agnostic, ensuring compatibility across a range of tools such as OpenAI's Codex, Google's Jules, and GitHub Copilot, while also being governed by the Agentic AI Foundation under the Linux Foundation. Unlike tool-specific files like CLAUDE.md, which cater to individual tools like Claude Code, AGENTS.md provides a unified, cross-tool standard that facilitates consistent behavior across different coding agents by including sections like project overview, setup commands, code style guidelines, and security considerations. This approach not only improves the quality and consistency of outputs from agents but also ensures that any changes in the tools do not disrupt the established workflow, making it a crucial infrastructure piece for teams using multiple agents.