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diagram-design
Editorial diagram design for Claude Code, Codex, GitHub Copilot, Cursor, Factory Droid, and Pi. 44 diagram types. Self-contained HTML + SVG. No shadows. No Mermaid slop.
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@cathrynlaveryAI & Agents
Plugin
codex-skill
Give Claude Code a "second opinion" by letting it consult OpenAI's Codex CLI for independent verification.
Plugin Signal64/100Solid
maintained84
capable23
documented100
adopted50
Install on Claude Code
> /plugin marketplace add cathrynlavery/codex-skill> /plugin install codex-skill@codex-skill
What's inside
Hook(1 hook)
README
Codex Skill for Claude Code
Give Claude Code a "second opinion" by letting it consult OpenAI's Codex CLI for independent verification.
What It Does
When Claude Code creates a plan, Codex automatically reviews it before you approve. Two AIs checking each other's work catches more edge cases.
Automatic review on:
- Every plan Claude creates (via hook)
- Architecture decisions
- Implementation approaches
Manual use for:
- Researching unfamiliar APIs or libraries
- Verifying complex code patterns
- Getting alternative perspectives
Prerequisites
Install Codex CLI:
npm install -g @openai/codex
Configure your OpenAI API key.
Supported Models
The skill supports the current visible Codex lineup. Automatic plan reviews do not pin a model; they inherit your configured Codex default.
| Model | Default effort | Supported efforts | Best for |
|---|---|---|---|
gpt-6-astra | low | low–ultra | Most capable option for difficult architecture, debugging, security, and long-horizon work |
gpt-5.6-sol | medium | low–ultra | Reliable everyday agentic workhorse |
gpt-5.6-terra | medium | low–ultra | Balanced everyday coding and review |
gpt-5.6-luna | medium | low–max | Fast and affordable checks |
gpt-5.5 | xhigh | low–xhigh | Previous-generation coding and general work |
Installation
Option A: Install as Claude Code plugin (recommended)
claude plugin marketplace add cathrynlavery/codex-skill
claude plugin install codex-skill@codex-skill
This auto-registers both the /codex skill and the automatic plan review hook. No manual configuration needed.
Option B: Manual installation
1. Install the skill
git clone https://github.com/cathrynlavery/codex-skill.git
mkdir -p ~/.claude/skills/codex
cp codex-skill/skills/codex/SKILL.md ~/.claude/skills/codex/
2. Set up automatic plan review
Copy the hook script:
mkdir -p ~/.claude/hooks
cp codex-skill/hooks/plan-review.sh ~/.claude/hooks/
chmod +x ~/.claude/hooks/plan-review.sh
Add to your ~/.claude/settings.json:
{
"hooks": {
"PostToolUse": [
{
"matcher": "ExitPlanMode",
"hooks": [
{
"type": "command",
"command": "~/.claude/hooks/plan-review.sh",
"timeout": 120
}
]
}
]
}
}
How It Works
┌─────────────┐ ┌─────────────┐ ┌─────────────┐
│ Claude │────>│ ExitPlanMode│────>│ Codex │
│ creates plan│ │ (hook) │ │ reviews │
└─────────────┘ └─────────────┘ └─────────────┘
│
v
┌─────────────┐
│ You approve │
│ with context│
└─────────────┘
The hook intercepts ExitPlanMode and reads the plan from tool_response.plan (the field where Claude Code stores the plan content). It passes the plan to Codex for review and displays the result before you approve.
Automatic plan reviews always use codex exec --sandbox read-only to restrict model-generated shell commands to read-only access. Manual consultations default to the same mode; explicit requests to implement changes use --sandbox workspace-write. If Codex fails, the hook reports that the review was skipped on stderr and exits successfully so your workflow can continue.
Codex reviews for:
- Potential issues or risks
- Missing steps
- Better alternatives
- Edge cases not addressed
Manual Usage
Invoke directly:
/codex
Or ask Claude:
"Can you verify this approach with Codex?" "Get a second opinion on this architecture"
These consultation requests use read-only mode. To have Codex make changes, explicitly request implementation, for example:
"Have Codex review and fix the parser bug, then run the relevant tests."
An explicit implementation request uses --sandbox workspace-write for edits and checks within the requested scope. No additional confirmation is needed for that same scope. Reviews do not automatically switch modes when a check needs to write files; they report the limitation. The automatic plan-review hook stays read-only even when the plan describes future edits.
The skill uses your configured Codex default. For the hardest questions (novel architecture, deep analysis, or security review), explicitly select gpt-6-astra with high or greater reasoning effort. For trivial fact checks, select gpt-5.6-luna.
Example Output
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
CODEX SECOND OPINION ON PLAN
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
LGTM - Plan covers the main implementation steps.
Minor suggestions:
- Consider adding error handling for the API timeout case
- Step 3 could be split into separate DB migration and code changes
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Troubleshooting
Plan review skipped: The hook prints codex-skill: plan review skipped (codex exited <status>; check installation, authentication, and configuration). on stderr when Codex fails, while remaining non-blocking. Make sure Codex CLI is installed (codex --version), on your PATH, authenticated, and configured correctly. Exit status 127 usually means the executable could not be found.
No plan content found: The hook reads from tool_response.plan (primary) with fallbacks to tool_response.filePath and filesystem search. If you're seeing issues, check that you're using a current version of Claude Code.
Development
Run the hook regression tests (requires Python 3, Bash, and jq; uses a stub Codex executable):
python3 -m unittest discover -s tests -v
License
MIT
File tree
More plugins by @cathrynlavery.
View @cathrynlavery’s profile@cathrynlaveryFAQ
codex-skill is a Claude Code plugin with 1 hand-picked skill, indexed on Flowy in the AI & Agents category. Install it with the command on its page. It includes codex. Its skills do not fire on their own yet. Request auto-invocation to have Flowy route them as you prompt. Free and open source.
- What is codex-skill?
- Give Claude Code a "second opinion" by letting it consult OpenAI's Codex CLI for independent verification.
- How do I install codex-skill?
- Run these in Claude Code: /plugin marketplace add cathrynlavery/codex-skill then /plugin install codex-skill@codex-skill. Then prompt normally.
- Does codex-skill auto-invoke its skills?
- Not yet. It is indexed on Flowy as a plain plugin. Request auto-invocation on its page and Flowy will route its skills for you as you prompt.
- Is codex-skill free?
- Yes. Flowy is free and open source, with nothing gated. You can read every skill in full before you install.
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