Codex Coder

Codex Coder Skill

Core Rule

ALL coding tasks MUST be executed via the Codex MCP — never write code manually. Always call mcp__codex-mcp__codex_task to delegate the work to Codex.

Trigger

Use this skill when the user asks to:

• Write or implement any code (features, functions, modules)
• Generate test cases (unit, integration, e2e)
• Create automation scripts (CI/CD, data pipelines, cron jobs, shell scripts)
• Refactor or fix existing code

Execution Steps

1. Identify the project directory

• Use the current working directory or ask the user if unclear
• Must be an absolute path to a git repository

2. Call Codex MCP to do the coding

Call mcp__codex-mcp__codex_task immediately with:

• project_dir: absolute path to the git project
• prompt: detailed task description (language, framework, file paths, expected behavior)

3. Review the output

Call mcp__codex-mcp__codex_review with the returned task ID to show the diff to the user.

4. Apply or Discard

• If user approves → call mcp__codex-mcp__codex_apply
• If user rejects → call mcp__codex-mcp__codex_discard and re-prompt with corrections

Check in-progress tasks

Call mcp__codex-mcp__codex_list to list all pending/active Codex tasks.

Prompt Guidelines for Codex

Write detailed prompts for best results:

Feature / Code:

Using [language/framework], implement [feature] in [file path].
Input: [describe], Output: [describe].
Follow existing code style and conventions.

Test Cases:

Write [Jest/pytest/Mocha] tests for [file/function].
Cover: happy path, edge cases, and error scenarios.
Mock external dependencies. Follow existing test structure.

Automation Script:

Create an automation script in [language] that [does X].
Trigger: [manual/cron/event]. Input: [source]. Output: [result].

Rules

• NEVER write code yourself — always use mcp__codex-mcp__codex_task
• ALWAYS call codex_review before codex_apply
• If the diff is wrong, call codex_discard and re-run with a better prompt
• Break large tasks into focused, single-concern prompts for best results