📘 Introduction

Codex can read, modify, and run code, but it still needs good project context. Without clear instructions, an AI coding agent may waste time exploring the wrong files, run the wrong test command, or make changes that do not match your team's workflow.

This is where AGENTS.md becomes useful. It is a Markdown file that gives Codex project-specific instructions: how the repository is structured, which commands to run, what coding style to follow, and which files should be handled carefully.

In this beginner-friendly guide, you will learn what AGENTS.md is in Codex, why it is needed, where to place it, and what to include in it.

💡 Why project instructions matter

AI coding agents work better when they do not have to guess your project rules. A repository can have many hidden expectations: test commands, linting tools, generated files, migration rules, API conventions, and review standards.

Codex can inspect a codebase, but a short instruction file can save time and reduce mistakes. Instead of rediscovering the same rules during every task, Codex can start with reusable guidance.

Think of AGENTS.md as onboarding notes for AI coding agents.

✅ Prerequisites

Before we start, you should have:

☑️ Basic curiosity about Codex
☑️ A local or GitHub code repository
☑️ Basic understanding of Markdown files
☑️ No advanced coding experience required

🧠 What is AGENTS.md?

AGENTS.md is a Markdown file that contains instructions for AI coding agents such as Codex.

It can describe:

  • how the project is organized
  • which commands run tests or linters
  • which coding patterns to follow
  • which files should not be edited
  • how to handle generated files, migrations, or secrets
  • what a safe finished task should include

It is not meant to replace your README. A README usually helps humans understand the project. AGENTS.md helps coding agents work inside the project more safely and consistently.

🤖 Why does Codex need AGENTS.md?

Codex can work on many different repositories, and every repository has different rules. One project may use pytest, another may use npm test, and another may require a special build command.

If those rules are not written down, Codex has to infer them. Sometimes that works. Sometimes it leads to avoidable mistakes.

AGENTS.md gives Codex a clearer starting point. It can tell Codex what matters before it edits files or runs commands.

📁 Where should AGENTS.md be placed?

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