ekino/docker-buildbox/codex

Codex Skill Guide

When to use this skill

Use this skill when:

• The user explicitly asks to run Codex CLI (e.g., "use codex to...", "run codex exec...")
• The user references OpenAI Codex or the Codex CLI tool by name
• The user wants code analysis or refactoring with configurable reasoning effort (low, medium, high)
• The user needs automated code editing with sandbox permissions (read-only, workspace-write, danger-full-access)

Running a Task

1. Ask the user (via AskUserQuestion) which model to run (gpt-5 or gpt-5-codex) AND which reasoning effort to use (low, medium, or high) 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="<low|medium|high>"
• --sandbox <read-only|workspace-write|danger-full-access>
• --full-auto
• -C, --cd <DIR>
• --skip-git-repo-check

1. 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 2>/dev/null
2. 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.
3. Run the command, capture stdout/stderr (filtered as appropriate), and summarize the outcome for the user.
4. 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

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 2>/dev/null. 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.