Codex Skill Guide

Running a Task

1. Always use model gpt-5.1-codex-max with reasoning effort high for all Codex runs:
   • Model: gpt-5.1-codex-max (mandatory, do not change)
   • Reasoning effort: high (mandatory, do not change)
   • If the user mentions other model names (gpt-5, gpt-5-codex-max, gpt-5-codex), always use gpt-5.1-codex-max instead.
   • Clearly state in your summary that model gpt-5.1-codex-max with high reasoning effort was used.
2. Select the sandbox mode required for the task; default to --sandbox read-only for analysis-only tasks, and use --sandbox workspace-write when edits are needed. Only consider --sandbox danger-full-access when the user’s request clearly requires network or broad system access.
3. Assemble the command with the appropriate options:
   • -m, --model <MODEL>
   • --config model_reasoning_effort="<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. When resuming don't use any configuration flags unless explicitly requested by the user e.g. if he species the model or the reasoning effort when requesting to resume a session. Resume syntax: echo "your prompt here" | codex exec --skip-git-repo-check resume --last 2>/dev/null. All flags have to 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

Following Up

• After every codex command, summarize what was done, propose concrete next steps, and, if needed, ask focused follow-up questions only about the task itself (not about model or reasoning-effort choices).
• 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 that gpt-5.1-codex-max with high reasoning effort was used, along with the 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 like --full-auto or --sandbox danger-full-access, make sure the user’s request clearly implies this level of automation or access; you do not need to ask them to choose model or reasoning-effort.
• When output includes warnings or partial results, summarize them and ask how to adjust using AskUserQuestion.