codex
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How to install codex?
skills-directory/skill-codex/codex
$npx -y skills add skills-directory/skill-codex --skill codexUse when the user asks to run Codex CLI (codex exec, codex resume) or references OpenAI Codex for code analysis, refactoring, or automated editing
SKILL.md
| 1 | # Codex Skill Guide |
| 2 | |
| 3 | ## Running a Task |
| 4 | 1. For a new session (resumes inherit the prior model/effort — see step 5), ask the user (via `AskUserQuestion`) which **model** AND which **reasoning effort** to use, in a **single prompt with two questions**. When the user expresses no preference, default to `gpt-5.6-sol` at `high`. |
| 5 | - **Model** — default `gpt-5.6-sol`: |
| 6 | - *GPT-5.6:* `gpt-5.6-sol` (frontier / most capable — **default**), `gpt-5.6-terra` (balanced, everyday), `gpt-5.6-luna` (fast & affordable) |
| 7 | - *Legacy (kept for compatibility):* `gpt-5.5`, `gpt-5.4`, `gpt-5.4-mini`, `gpt-5.3-codex-spark`, `gpt-5.3-codex` |
| 8 | - **Reasoning effort** — default `high`: `low`, `medium`, `high`, `xhigh`, `max`, `ultra`. |
| 9 | - `max`/`ultra` require a GPT-5.6 model; `ultra` is only on `sol`/`terra` (`luna` caps at `max`); legacy models cap at `xhigh`. |
| 10 | - `ultra` = maximum reasoning **with automatic task delegation** (slowest and most expensive — reserve for the hardest jobs). |
| 11 | - If the chosen effort exceeds the chosen model's maximum, fall back to that model's highest supported effort and tell the user. |
| 12 | 2. Select the sandbox mode required for the task; default to `--sandbox read-only` unless edits or network access are necessary. |
| 13 | 3. Assemble the command with the appropriate options: |
| 14 | - `-m, --model <MODEL>` |
| 15 | - `--config model_reasoning_effort="<low|medium|high|xhigh|max|ultra>"` (max/ultra only on GPT-5.6 models; ultra only on sol/terra — see step 1) |
| 16 | - `--sandbox <read-only|workspace-write|danger-full-access>` |
| 17 | - `--full-auto` |
| 18 | - `-C, --cd <DIR>` |
| 19 | - `--skip-git-repo-check` |
| 20 | - `"your prompt here"` (as final positional argument) |
| 21 | 4. Always use --skip-git-repo-check. |
| 22 | 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. |
| 23 | 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. |
| 24 | 7. **IMPORTANT (stdin)**: `codex exec` always reads stdin and concatenates it with the positional prompt -- even when the prompt is fully supplied as a positional argument. If stdin is not closed, codex blocks forever. When invoking from a harness (background tasks, hooks, scripts where stdin is not a TTY but also not closed), explicitly redirect stdin: append `</dev/null` to the command, e.g. `codex exec ... "prompt" </dev/null 2>/dev/null`. Symptom of getting this wrong: zero bytes of stdout, zero CPU accumulated, process appears hung indefinitely. |
| 25 | 8. Run the command, capture stdout/stderr (filtered as appropriate), and summarize the outcome for the user. |
| 26 | 9. **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." |
| 27 | |
| 28 | ### Quick Reference |
| 29 | | Use case | Sandbox mode | Key flags | |
| 30 | | --- | --- | --- | |
| 31 | | Read-only review or analysis | `read-only` | `--sandbox read-only 2>/dev/null` | |
| 32 | | Apply local edits | `workspace-write` | `--sandbox workspace-write --full-auto 2>/dev/null` | |
| 33 | | Permit network or broad access | `danger-full-access` | `--sandbox danger-full-access --full-auto 2>/dev/null` | |
| 34 | | Resume recent session | Inherited from original | `echo "prompt" \| codex exec --skip-git-repo-check resume --last 2>/dev/null` (no flags allowed) | |
| 35 | | Run from another directory | Match task needs | `-C <DIR>` plus other flags `2>/dev/null` | |
| 36 | |
| 37 | ## Execution timeouts |
| 38 | |
| 39 | Codex produces **no intermediate output** — it writes the result only at completion. If the process is killed before finishing, the output file is silently empty (no error). |
| 40 | |
| 41 | **Preferred approach:** run synchronously — eliminates timeout risk entirely and the conversation waits for the result anyway. |
| 42 | |
| 43 | **If running in background**, set the execution timeout based on reasoning effort: |
| 44 | |
| 45 | | Reasoning effort | Timeout | |
| 46 | |---|---| |
| 47 | | `low` | 150s | |
| 48 | | `medium` | 300s | |
| 49 | | `high` | 600s | |
| 50 | | `xhigh` | 1200s | |
| 51 | | `max` | 1800s | |
| 52 | | `ultra` | 1800s | |
| 53 | |
| 54 | ## Following Up |
| 55 | - After every `codex` command, immediately use `AskUserQuestion` to confirm next steps, collect clarifications, or decide whether to resume with `codex exec resume --last`. |
| 56 | - 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. |
| 57 | - Resta |
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