Runs external LLM code reviews (OpenAI Codex or Google Gemini CLI) on uncommitted changes, branch diffs, or specific commits. Use when the user asks for a second opinion, external review, codex review, gemini review, or mentions /second-opinion.
Runs external LLM code reviews (OpenAI Codex or Google Gemini CLI) on uncommitted changes, branch diffs, or specific commits. Use when the user asks for a second opinion, external review, codex review, gemini review, or mentions /second-opinion.
allowed-tools
Bash Read Glob Grep AskUserQuestion
Second Opinion
Shell out to external LLM CLIs for an independent code review powered by
a separate model. Supports OpenAI Codex CLI and Google Gemini CLI.
When to Use
Getting a second opinion on code changes from a different model
Reviewing branch diffs before opening a PR
Checking uncommitted work for issues before committing
Running a focused review (security, performance, error handling)
Comparing review output from multiple models
When NOT to Use
Neither Codex CLI nor Gemini CLI is installed
No API key or subscription configured for either tool
Reviewing non-code files (documentation, config)
You want Claude's own review (just ask Claude directly)
Safety Note
Gemini CLI is invoked with --yolo, which auto-approves all
tool calls without confirmation. This is required for headless
(non-interactive) operation but means Gemini will execute any
tool actions its extensions request without prompting.
Quick Reference
# Codex (headless exec with structured JSON output)
codex exec --sandbox read-only --ephemeral \
--output-schema codex-review-schema.json \
-o "$output_file" - < "$prompt_file"
# Gemini (code review extension)
gemini -p "/code-review" --yolo -e code-review
# Gemini (headless with diff — see references/ for full pattern)
git diff HEAD > /tmp/review-diff.txt
{ printf '%s\n\n' 'Review this diff for issues.'; cat /tmp/review-diff.txt; } \
| gemini -p - --yolo -m gemini-3.1-pro-preview
Invocation
1. Gather context interactively
Use AskUserQuestion to collect review parameters in one shot.
Adapt the questions based on what the user already provided
in their invocation (skip questions they already answered).
Combine all applicable questions into a single AskUserQuestion
call (max 4 questions).
Question 1 — Tool (skip if user already specified):
header: "Review tool"
question: "Which tool should run the review?"
options:
- "Both Codex and Gemini (Recommended)" → run both in parallel
- "Codex only" → codex exec
- "Gemini only" → gemini CLI
Question 2 — Scope (skip if user already specified):
header: "Review scope"
question: "What should be reviewed?"
options:
- "Uncommitted changes" → git diff HEAD + untracked files
- "Branch diff vs main" → git diff <branch>...HEAD (auto-detect default branch)
- "Specific commit" → git diff <sha>~1..<sha> (follow up for SHA)
Question 3 — Project context (skip if neither CLAUDE.md nor AGENTS.md exists):
Check for CLAUDE.md first, then AGENTS.md in the repo root.
Only show this question if at least one exists.
header: "Project context"
question: "Include project conventions file so the review
checks against your standards?"
options:
- "Yes, include it"
- "No, standard review"
Question 4 — Review focus (always ask):
header: "Review focus"
question: "Any specific focus areas for the review?"
options:
- "General review" → no custom prompt
- "Security & auth" → security-focused prompt
- "Performance" → performance-focused prompt
- "Error handling" → error handling-focused prompt
2. Run the tool directly
Do not pre-check tool availability. Run the selected tool
immediately. If the command fails with "command not found" or
an extension is missing, report the install command from the
Error Handling table below and skip that tool (if "Both" was
selected, run only the available one).
Diff Preview
After collecting answers, show the diff stats:
# For uncommitted (tracked + untracked):
git diff --stat HEAD
git ls-files --others --exclude-standard
# For branch diff:
git diff --stat <branch>...HEAD
# For specific commit:
git diff --stat <sha>~1..<sha>
If the diff is empty, stop and tell the user.
If the diff is very large (>2000 lines changed), warn the user
and ask whether to proceed or narrow the scope.
Skipping Inapplicable Checks
After determining the diff scope, skip checks that don't apply
to the files actually changed.
Dependency Scanning
Only run /security:scan-deps when the diff touches dependency
manifest files. Check with:
If no dependency files are in the diff, skip the scan even when
security focus is selected. The scan analyzes the entire project's
dependency tree regardless of diff scope, so it adds significant
time for zero value when dependencies weren't touched.
Auto-detect Default Branch
For branch diff scope, detect the default branch name:
git symbolic-ref refs/remotes/origin/HEAD 2>/dev/null \
| sed 's@^refs/remotes/origin/@@' || echo main
Codex Invocation
See references/codex-invocation.md
for full details on command syntax, prompt assembly, and the
structured output schema.
Summary:
Uses codex exec (not codex review) for headless operation
Model: gpt-5.5, reasoning: xhigh
Uses OpenAI's published code review prompt (fine-tuned into the model)
Diff is generated manually and piped via stdin with the prompt
--output-schema produces structured JSON findings
-o captures only the final message (no thinking/exec noise)
All three scopes (uncommitted, branch, commit) support project
context and focus instructions (no limitations)
Falls back to gpt-5.4 on auth errors
Output is clean JSON — parse and present findings by priority
For uncommitted general review: gemini -p "/code-review" --yolo -e code-review
For branch/commit diffs: pipe git diff into gemini -p
Security extension name is gemini-cli-security (not security)
/security:analyze is interactive-only — use -p with a
security prompt instead
Run /security:scan-deps only when security focus is selected
AND the diff touches dependency manifest files (see Diff-Aware
Optimizations)
Set timeout: 600000 on the Bash call
Scope mapping for git diff (Gemini has no built-in scope flags):
Scope
Diff command
Uncommitted
git diff HEAD + untracked (see codex-invocation.md)
Branch diff
git diff <branch>...HEAD
Specific commit
git diff <sha>~1..<sha>
Running Both
When the user picks "Both" (the default):
Run Codex and Gemini in parallel — issue both Bash tool
calls in a single response. Both commands are read-only
(they review diffs via external APIs) so there is no
shared state or git lock contention.
Collect both results, then present with clear headers:
