The AGENTS.md file that stops AI coding tools from overbuilding

Short answer

AGENTS.md is a plain-text instruction file for AI coding agents. It tells the agent how to work inside your repo before it starts editing.

Use it to define setup commands, project structure, style rules, testing commands, review expectations, and do-not-change areas. The goal is not more documentation. The goal is fewer agent guesses and a safer agent workflow.

Why this matters

AI coding tools are powerful, but they can overbuild when the repo has no local rules. They may invent patterns, add unnecessary abstractions, skip tests, or change unrelated files.

OpenAI’s AGENTS.md guide describes AGENTS.md as a way to provide instructions and context to Codex. Anthropic’s Claude Code memory docs describe a similar idea with CLAUDE.md files for project memory and instructions.

Sources: OpenAI: AGENTS.md guide, Anthropic: Claude Code memory

What to include

A useful AGENTS.md should be short enough to read and specific enough to change behavior.

• Project purpose: what the repo does.
• Setup commands: install, run, build, and test.
• Code style: formatting, naming, components, patterns, and folder rules.
• Testing rules: what to run before calling work done.
• Design rules: UI standards, spacing, accessibility, and visual QA requirements.
• Do-not-change rules: files, flows, or conventions the agent should not touch casually.
• Review checklist: what the agent should verify before final response.

AGENTS.md vs CLAUDE.md

AGENTS.md is commonly used by Codex-style coding agents. CLAUDE.md is commonly used by Claude Code. The underlying idea is the same: repo-specific instructions that travel with the project.

If you use multiple tools, keep the important rules consistent. You do not want Codex and Claude following two different versions of your repo conventions.

The anti-overbuild rules

The most useful part of AGENTS.md is often the do-not-overbuild section.

Coding agents can solve small problems with big architecture if you do not constrain them. Add rules that force the smallest useful change and require reuse of existing patterns.

• Prefer existing patterns over new abstractions.
• Keep edits scoped to the requested behavior.
• Do not add dependencies without explaining why.
• Do not rewrite working components just to clean them up.
• Do not change unrelated files.
• Run the narrowest useful test or build check.
• If visual UI changes are made, inspect the rendered page before finishing.

Starter AGENTS.md

Use this structure as a first pass.

• # Project overview
• # Setup commands
• # Build and test commands
• # Code style
• # UI and visual QA rules
• # Files or areas to avoid changing
• # How to report final work

Query fan-out this page answers

The seed query is "what is AGENTS.md?" The useful fan-out is about what to include, how it differs from CLAUDE.md, and how it prevents AI coding tools from overbuilding.

That is why this page gives the purpose, file comparison, guardrails, starter structure, and links to official docs.

Reference links

This topic came from TikTok source 14 and is grounded in official OpenAI and Anthropic documentation.

Sources: TikTok source 14 idea trigger, OpenAI: AGENTS.md guide, OpenAI: Codex best practices, Anthropic: Claude Code memory

Final answer

AGENTS.md is one of the simplest ways to make AI coding tools behave better inside a real repo.

Keep it short, specific, and practical: setup, style, tests, do-not-change rules, and review expectations. The goal is to make the agent ask fewer questions, guess less, and ship smaller safer changes.