Codex Skill Guide

This skill enables the use of Codex CLI for code analysis, refactoring, and automated editing tasks.

When to Use This Skill

Use this skill when the user:

Running a Task

1. Ask the user (via `AskUserQuestion`) which model to run (`gpt-5.2-codex` or `gpt-5.2`) AND which reasoning effort to use (`xhigh`, `high`, `medium`, or `low`) in a **single prompt with two questions**.

2. Select the sandbox mode required for the task; default to `--sandbox read-only` unless edits or network access are necessary.

3. Assemble the command with the appropriate options:

- `-m, --model <MODEL>`

- `--config model_reasoning_effort="<xhigh|high|medium|low>"`

- `--sandbox <read-only|workspace-write|danger-full-access>`

- `--full-auto`

- `-C, --cd <DIR>`

- `--skip-git-repo-check`

4. Always use --skip-git-repo-check.

5. When continuing a previous session:

- Use `codex exec --skip-git-repo-check resume --last` via stdin

- Don't use any configuration flags unless explicitly requested by the user (e.g., if they specify the model or reasoning effort when requesting to resume)

- Resume syntax: `echo "your prompt here" | codex exec --skip-git-repo-check resume --last 2>/dev/null`

- All flags must be inserted between `exec` and `resume`

6. **IMPORTANT**: By default, append `2>/dev/null` to all `codex exec` commands to suppress thinking tokens (stderr). Only show stderr if the user explicitly requests to see thinking tokens or if debugging is needed.

7. Run the command, capture stdout/stderr (filtered as appropriate), and summarize the outcome for the user.

8. **After Codex completes**, inform the user: "You can resume this Codex session at any time by saying 'codex resume' or asking me to continue with additional analysis or changes."

Quick Reference

| Use case | Sandbox mode | Key flags |

| --- | --- | --- |

| Read-only review or analysis | `read-only` | `--sandbox read-only 2>/dev/null` |

| Apply local edits | `workspace-write` | `--sandbox workspace-write --full-auto 2>/dev/null` |

| Permit network or broad access | `danger-full-access` | `--sandbox danger-full-access --full-auto 2>/dev/null` |

| Resume recent session | Inherited from original | `echo "prompt" \\| codex exec --skip-git-repo-check resume --last 2>/dev/null` |

| Run from another directory | Match task needs | `-C <DIR>` plus other flags `2>/dev/null` |

Following Up

Error Handling

Examples

Read-only Analysis

```bash

codex exec --skip-git-repo-check \

-m gpt-5.2-codex \

--config model_reasoning_effort="high" \

--sandbox read-only \

"Analyze the code structure and identify potential improvements" \

2>/dev/null

```

Apply Edits

```bash

codex exec --skip-git-repo-check \

-m gpt-5.2 \

--config model_reasoning_effort="medium" \

--sandbox workspace-write \

--full-auto \

"Refactor the authentication module to use async/await" \

2>/dev/null

```

Resume Session

```bash

echo "Now add error handling to the refactored code" | \

codex exec --skip-git-repo-check resume --last 2>/dev/null

```

Notes