HALLUCINATE.md landed on GitHub this week with a deceptively simple pitch: place one file in your repository and tell AI coding agents to stop making things up. The standard—maintained by the HALLUCINATE.md Foundation, an independent open-source initiative—consists of exactly three words: "Do not hallucinate!" No schema, no configuration flags, no dependencies. Just a markdown directive that every major AI coding agent can parse alongside your existing project files.

The Philosophy Behind the File

The project's maintainers draw a clear distinction between HALLUCINATE.md and its cousin AGENTS.md. Where AGENTS.md provides general instructions for how agents should operate within a codebase, HALLUCINATE.md targets one specific problem: fabrication. "AGENTS.md tells agents how to work," the documentation states. "HALLUCINATE.md tells agents what not to invent." This separation of concerns is intentional—by keeping the standard laser-focused on hallucination rather than bloating it with general best practices, the maintainers argue the directive stays impossible to ignore or misread.

Compatibility With Major AI Coding Agents

The standard claims support across essentially every major player in the AI coding assistant space: Claude (Anthropic), Cursor, GitHub Copilot, Windsurf, Devin (Cognition), Codex (OpenAI), Gemini (Google), Aider, Amazon Q, and Cody (Sourcegraph) all allegedly parse HALLUCINATE.md alongside project configuration files. The documentation notes that the file is read in the same context as other markdown-based config files—README.md, CONTRIBUTING.md, and so on—so it factors into agent decision-making without requiring any special integration work.

Why Simplicity Is the Point

The FAQ addresses the obvious skepticism head-on: "Does this actually work?" The answer leans hard into simplicity as a design philosophy. Because there's no required format beyond the three-word directive itself, there's nothing for an agent to misparse or deprioritize. If hallucinations still occur after adding HALLUCINATE.md, the troubleshooting advice is straightforward—ensure the filename matches exactly (case-sensitive), and add copies of the file to more directories where agents operate.

Key Takeaways

  • HALLUCINATE.md requires only "Do not hallucinate!" as content—no schema or structured format needed
  • The standard works with Claude, Cursor, Copilot, Windsurf, Devin, Codex, Gemini, Aider, Amazon Q, and Cody out of the box
  • Place the file in your repository root, subdirectories, or both for maximum coverage
  • Maintained by the independent HALLUCINATE.md Foundation under MIT licensing

The Bottom Line

Look, I'm skeptical too—but the elegance here is hard to argue with. If a three-word directive genuinely moves the needle on hallucination rates across these agents, that's a net win for every developer who's watched an AI confidently propose non-existent API endpoints or invent function signatures from whole cloth. Whether this catches on depends entirely on whether real-world testing backs up the theory.