Codex Skill Guide

When to Use Codex

Use Codex proactively for:

For analysis, refactoring, debugging, or any task requiring file access and reasoning.

For reviewing diffs, uncommitted changes, or comparing against branches.

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Ask the user (via AskUserQuestion) which model to run (gpt-5.2-codex or gpt-5.2) AND which reasoning effort to use (xhigh, high, medium, or low) in a single prompt with two questions.
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Select the sandbox mode required for the task; default to --sandbox read-only unless edits or network access are necessary.
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Assemble the command with the appropriate options:
- •-m, --model <MODEL>
- •--config model_reasoning_effort="<xhigh|high|medium|low>"
- •--sandbox <read-only|workspace-write|danger-full-access>
- •--full-auto
- •-C, --cd <DIR>
- •--skip-git-repo-check
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Always use --skip-git-repo-check.
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IMPORTANT: Append 2>/dev/null to suppress thinking tokens (stderr). Only show stderr if debugging is needed.
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Run the command, capture output, and summarize the outcome for the user.
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After completion, inform the user: "You can resume this Codex session at any time by saying 'codex resume'."

Use case	Sandbox mode	Command
Read-only analysis	`read-only`	`codex exec --skip-git-repo-check -m MODEL --sandbox read-only "prompt" 2>/dev/null`
Apply local edits	`workspace-write`	`codex exec --skip-git-repo-check -m MODEL --sandbox workspace-write --full-auto "prompt" 2>/dev/null`
Network/broad access	`danger-full-access`	`codex exec --skip-git-repo-check -m MODEL --sandbox danger-full-access --full-auto "prompt" 2>/dev/null`
Resume session	Inherited	`echo "prompt" \| codex exec --skip-git-repo-check resume --last 2>/dev/null`
Different directory	Match task	`codex exec --skip-git-repo-check -C <DIR> -m MODEL --sandbox read-only "prompt" 2>/dev/null`

When continuing a previous session:

bash

echo "your prompt here" | codex exec --skip-git-repo-check resume --last 2>/dev/null

Use for code review tasks. No need to ask for model/reasoning - review uses sensible defaults.

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Ask the user (via AskUserQuestion) what to review:
- •Uncommitted changes - all local modifications
- •Against a branch - compare to base branch (e.g., main)
- •Specific commit - review a commit SHA
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Optionally ask for custom review focus (security, performance, conventions, etc.)
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Run the appropriate command and summarize findings.

Use case	Command
Uncommitted changes	`codex review --uncommitted`
Against main branch	`codex review --base main`
Against specific branch	`codex review --base feature/xyz`
Specific commit	`codex review --commit abc123`
With custom focus	`codex review --uncommitted "Focus on security"`
With title context	`codex review --base main --title "Add user auth"`

bash

# Use specific model
codex review --uncommitted -c model="o3"

Situation	Use
"Review my changes"	`codex review --uncommitted`
"Review this PR"	`codex review --base main`
"Analyze this architecture"	`codex exec`
"Help me debug this"	`codex exec`
"Refactor this code"	`codex exec` with workspace-write
"Is this secure?"	`codex review` for diffs, `codex exec` for deep analysis

•After every command, use AskUserQuestion to confirm next steps or collect clarifications
•For exec: offer to resume with codex exec resume --last
•For review: offer to help address specific findings
•Restate the chosen configuration when proposing follow-up actions

•Stop and report failures on non-zero exit; request direction before retrying
•Before using high-impact flags (--full-auto, --sandbox danger-full-access), ask user permission via AskUserQuestion unless already given
•Summarize warnings or partial results and ask how to adjust