Codex Skill Guide
Running a Task
- Always use model
gpt-5.1-codex-maxwith reasoning efforthighfor 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-maxinstead. - Clearly state in your summary that model
gpt-5.1-codex-maxwithhighreasoning effort was used.
- Model:
- Select the sandbox mode required for the task; default to
--sandbox read-onlyfor analysis-only tasks, and use--sandbox workspace-writewhen edits are needed. Only consider--sandbox danger-full-accesswhen the user’s request clearly requires network or broad system access. - 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
- Always use --skip-git-repo-check.
- When continuing a previous session, use
codex exec --skip-git-repo-check resume --lastvia 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. - IMPORTANT: By default, append
2>/dev/nullto allcodex execcommands to suppress thinking tokens (stderr). Only show stderr if the user explicitly requests to see thinking tokens or if debugging is needed. - Run the command, capture stdout/stderr (filtered as appropriate), and summarize the outcome for the user.
- 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 (no flags allowed) |
| Run from another directory | Match task needs | -C <DIR> plus other flags 2>/dev/null |
Following Up
- After every
codexcommand, 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-maxwithhighreasoning effort was used, along with the sandbox mode, when proposing follow-up actions.
Error Handling
- Stop and report failures whenever
codex --versionor acodex execcommand exits non-zero; request direction before retrying. - Before you use high-impact flags like
--full-autoor--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.
