Codex Skill Guide
Running a Task
- Default to
gpt-5.2 model. Ask the user (via AskUserQuestion) which reasoning effort to use (xhigh,high, medium, or low). User can override model if needed (see Model Options below).
- 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="<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 --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.
- 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.
- 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 |
Model Options
| Model |
Best for |
Context window |
Key features |
gpt-5.2-max |
Max model: Ultra-complex reasoning, deep problem analysis |
400K input / 128K output |
76.3% SWE-bench, adaptive reasoning, $1.25/$10.00 |
gpt-5.2 ⭐ |
Flagship model: Software engineering, agentic coding workflows |
400K input / 128K output |
76.3% SWE-bench, adaptive reasoning, $1.25/$10.00 |
gpt-5.2-mini |
Cost-efficient coding (4x more usage allowance) |
400K input / 128K output |
Near SOTA performance, $0.25/$2.00 |
gpt-5.1-thinking |
Ultra-complex reasoning, deep problem analysis |
400K input / 128K output |
Adaptive thinking depth, runs 2x slower on hardest tasks |
GPT-5.2 Advantages: 76.3% SWE-bench (vs 72.8% GPT-5), 30% faster on average tasks, better tool handling, reduced hallucinations, improved code quality. Knowledge cutoff: September 30, 2024.
Reasoning Effort Levels:
xhigh - Ultra-complex tasks (deep problem analysis, complex reasoning, deep understanding of the problem)high - Complex tasks (refactoring, architecture, security analysis, performance optimization)medium - Standard tasks (refactoring, code organization, feature additions, bug fixes)low - Simple tasks (quick fixes, simple changes, code formatting, documentation)
Cached Input Discount: 90% off ($0.125/M tokens) for repeated context, cache lasts up to 24 hours.
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.
CLI Version
Requires Codex CLI v0.57.0 or later for GPT-5.2 model support. The CLI defaults to gpt-5.2 on macOS/Linux and gpt-5.2 on Windows. Check version: codex --version
Use /model slash command within a Codex session to switch models, or configure default in ~/.codex/config.toml.
1---2name: codex3description: Use when the user asks to run Codex CLI (codex exec, codex resume) or references OpenAI Codex for code analysis, refactoring, or automated editing. Uses GPT-5.2 by default for state-of-the-art software engineering.4---56# Codex Skill Guide78## Running a Task91. Default to `gpt-5.2` model. Ask the user (via `AskUserQuestion`) which reasoning effort to use (`xhigh`,`high`, `medium`, or `low`). User can override model if needed (see Model Options below).102. Select the sandbox mode required for the task; default to `--sandbox read-only` unless edits or network access are necessary.113. Assemble the command with the appropriate options:12 - `-m, --model <MODEL>`13 - `--config model_reasoning_effort="<high|medium|low>"`14 - `--sandbox <read-only|workspace-write|danger-full-access>`15 - `--full-auto`16 - `-C, --cd <DIR>`17 - `--skip-git-repo-check`183. Always use --skip-git-repo-check.194. 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.205. **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.216. Run the command, capture stdout/stderr (filtered as appropriate), and summarize the outcome for the user.227. **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."2324### Quick Reference25| Use case | Sandbox mode | Key flags |26| --- | --- | --- |27| Read-only review or analysis | `read-only` | `--sandbox read-only 2>/dev/null` |28| Apply local edits | `workspace-write` | `--sandbox workspace-write --full-auto 2>/dev/null` |29| Permit network or broad access | `danger-full-access` | `--sandbox danger-full-access --full-auto 2>/dev/null` |30| Resume recent session | Inherited from original | `echo "prompt" \| codex exec --skip-git-repo-check resume --last 2>/dev/null` (no flags allowed) |31| Run from another directory | Match task needs | `-C <DIR>` plus other flags `2>/dev/null` |3233## Model Options3435| Model | Best for | Context window | Key features |36| --- | --- | --- | --- |37| `gpt-5.2-max` | **Max model**: Ultra-complex reasoning, deep problem analysis | 400K input / 128K output | 76.3% SWE-bench, adaptive reasoning, $1.25/$10.00 |38| `gpt-5.2` ⭐ | **Flagship model**: Software engineering, agentic coding workflows | 400K input / 128K output | 76.3% SWE-bench, adaptive reasoning, $1.25/$10.00 |39| `gpt-5.2-mini` | Cost-efficient coding (4x more usage allowance) | 400K input / 128K output | Near SOTA performance, $0.25/$2.00 |40| `gpt-5.1-thinking` | Ultra-complex reasoning, deep problem analysis | 400K input / 128K output | Adaptive thinking depth, runs 2x slower on hardest tasks |4142**GPT-5.2 Advantages**: 76.3% SWE-bench (vs 72.8% GPT-5), 30% faster on average tasks, better tool handling, reduced hallucinations, improved code quality. Knowledge cutoff: September 30, 2024.4344**Reasoning Effort Levels**:45- `xhigh` - Ultra-complex tasks (deep problem analysis, complex reasoning, deep understanding of the problem)46- `high` - Complex tasks (refactoring, architecture, security analysis, performance optimization)47- `medium` - Standard tasks (refactoring, code organization, feature additions, bug fixes)48- `low` - Simple tasks (quick fixes, simple changes, code formatting, documentation)4950**Cached Input Discount**: 90% off ($0.125/M tokens) for repeated context, cache lasts up to 24 hours.5152## Following Up53- After every `codex` command, immediately use `AskUserQuestion` to confirm next steps, collect clarifications, or decide whether to resume with `codex exec resume --last`.54- 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.55- Restate the chosen model, reasoning effort, and sandbox mode when proposing follow-up actions.5657## Error Handling58- Stop and report failures whenever `codex --version` or a `codex exec` command exits non-zero; request direction before retrying.59- 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.60- When output includes warnings or partial results, summarize them and ask how to adjust using `AskUserQuestion`.6162## CLI Version6364Requires Codex CLI v0.57.0 or later for GPT-5.2 model support. The CLI defaults to `gpt-5.2` on macOS/Linux and `gpt-5.2` on Windows. Check version: `codex --version`6566Use `/model` slash command within a Codex session to switch models, or configure default in `~/.codex/config.toml`.
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