How do I install the Codex skill?

Run npx skillmds add majiayu000/codex-4 in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Codex safe to use?

This skill has not completed SkillMD's automated safety review yet. Capability flags: docs only. SkillMD never runs a skill's scripts for you; review the SKILL.md before installing.

Which AI agents work with Codex?

This skill is tagged as working with Claude Code, Claude.ai, OpenAI Codex. SKILL.md is an open format, so most agents that read a skills directory can load it too.

Is Codex free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

majiayu000 (@majiayu000) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Codex by majiayu000 — Agent Skill

Name: Codex
Rating: 4.2 (5 reviews)
Author: majiayu000

File contents

Codex Skill Guide

Running a Task

Ask the user (via AskUserQuestion) which model to run: gpt-5 or gpt-5-codex.
Ask the user (via AskUserQuestion) which reasoning effort to use: low, medium, or high.
Select the sandbox mode required for the task; default to --sandbox read-only unless edits or network access are necessary.
Assemble the command with the appropriate options:
- -m, --model <MODEL>
- --config model_reasoning_effort="<low|medium|high>"
- --sandbox <read-only|workspace-write|danger-full-access>
- --full-auto
- -C, --cd <DIR>
- --skip-git-repo-check
When continuing a previous session, use codex exec resume --last via stdin. IMPORTANT: When resuming, you CANNOT specify model, reasoning effort, or other flags—the session retains all settings from the original run. Resume syntax: echo "your prompt here" | codex exec resume --last
Run the command, capture stdout/stderr, and summarize the outcome for the user.

Quick Reference

Use case	Sandbox mode	Key flags
Read-only review or analysis	`read-only`	`--sandbox read-only`
Apply local edits	`workspace-write`	`--sandbox workspace-write --full-auto`
Permit network or broad access	`danger-full-access`	`--sandbox danger-full-access --full-auto`
Resume recent session	Inherited from original	`echo "prompt" \| codex exec resume --last` (no flags allowed)
Run from another directory	Match task needs	`-C <DIR>` plus other flags

Following Up

After every codex command, immediately use AskUserQuestion to confirm next steps, collect clarifications, or decide whether to resume with codex exec resume --last.
When resuming, pipe the new prompt via stdin: echo "new prompt" | codex exec resume --last. The resumed session automatically uses the same model, reasoning effort, and sandbox mode from the original session.
Restate the chosen model, reasoning effort, and sandbox mode when proposing follow-up actions.

Error Handling

Stop and report failures whenever codex --version or a codex exec command exits non-zero; request direction before retrying.
Before you use high-impact flags (--full-auto, --sandbox danger-full-access, --skip-git-repo-check) ask the user for permission using AskUserQuestion unless it was already given.
When output includes warnings or partial results, summarize them and ask how to adjust using AskUserQuestion.

---name: codex-4description: Use when the user asks to run Codex CLI (codex exec, codex resume) or references OpenAI Codex for code analysis, refactoring, or automated editing--- # Codex Skill Guide ## Running a Task 1. Ask the user (via `AskUserQuestion`) which model to run: `gpt-5` or `gpt-5-codex`. 2. Ask the user (via `AskUserQuestion`) which reasoning effort to use: `low`, `medium`, or `high`. 3. Select the sandbox mode required for the task; default to `--sandbox read-only` unless edits or network access are necessary. 4. Assemble the command with the appropriate options: - `-m, --model <MODEL>` - `--config model_reasoning_effort="<low|medium|high>"` - `--sandbox <read-only|workspace-write|danger-full-access>` - `--full-auto` - `-C, --cd <DIR>` - `--skip-git-repo-check` 5. When continuing a previous session, use `codex exec resume --last` via stdin. **IMPORTANT**: When resuming, you CANNOT specify model, reasoning effort, or other flags—the session retains all settings from the original run. Resume syntax: `echo "your prompt here" | codex exec resume --last` 6. Run the command, capture stdout/stderr, and summarize the outcome for the user. ### Quick Reference | Use case | Sandbox mode | Key flags | | --- | --- | --- | | Read-only review or analysis | `read-only` | `--sandbox read-only` | | Apply local edits | `workspace-write` | `--sandbox workspace-write --full-auto` | | Permit network or broad access | `danger-full-access` | `--sandbox danger-full-access --full-auto` | | Resume recent session | Inherited from original | `echo "prompt" \| codex exec resume --last` (no flags allowed) | | Run from another directory | Match task needs | `-C <DIR>` plus other flags | ## Following Up - After every `codex` command, immediately use `AskUserQuestion` to confirm next steps, collect clarifications, or decide whether to resume with `codex exec resume --last`. - When resuming, pipe the new prompt via stdin: `echo "new prompt" | codex exec resume --last`. The resumed session automatically uses the same model, reasoning effort, and sandbox mode from the original session. - Restate the chosen model, reasoning effort, and sandbox mode when proposing follow-up actions. ## Error Handling - Stop and report failures whenever `codex --version` or a `codex exec` command exits non-zero; request direction before retrying. - Before you use high-impact flags (`--full-auto`, `--sandbox danger-full-access`, `--skip-git-repo-check`) ask the user for permission using AskUserQuestion unless it was already given. - When output includes warnings or partial results, summarize them and ask how to adjust using `AskUserQuestion`.

Frequently asked questions