External LLM Code Review
Audience: Developers seeking second-opinion code reviews from external LLMs. Goal: Invoke external LLM CLIs in sandbox/read-only mode to review code changes, then present structured findings for comparison with Claude's review.
When to Use
- High-stakes code changes (security, breaking changes, architecture shifts)
- Validating Claude's code review with diverse AI perspectives
- Surfacing blind spots through cross-model review
- When you want explicit control over review focus areas
General Workflow
- Determine review scope (uncommitted, staged, branch, specific commit)
- Gather the diff and project context (CLAUDE.md, lessons)
- Build a review prompt with context, focus areas, and the diff
- Execute the external CLI in sandbox/read-only mode
- Parse and structure findings by severity
Gathering the Diff
Based on the requested scope:
# Uncommitted changes (default)
git diff HEAD
# Staged only
git diff --cached
# Against base branch
git diff main...HEAD
# Specific commit
git show <sha>
# Specific files
git diff -- path/to/file.rbGathering Project Context
# Project conventions
cat CLAUDE.md 2>/dev/null | head -200
# Institutional memory / lessons
ls .agents/lessons/*.md 2>/dev/null && \
head -50 .agents/lessons/*.mdLessons provide project-specific patterns and anti-patterns discovered during development.
Building the Review Prompt
Construct a prompt that includes:
## Project Context
<Insert relevant CLAUDE.md sections>
## Project Lessons
<Insert relevant lessons from .agents/lessons/ if available>
## Focus Areas
<Insert user-specified focus areas, or use defaults:>
1. Logic errors and bugs
2. Security vulnerabilities
3. Performance issues
4. Error handling gaps
5. Code clarity and maintainability
## Changes to Review
<Insert git diff>
## Instructions
Review the changes above. For each issue found:
1. Specify the file and line number
2. Describe the issue clearly
3. Suggest a fix if applicable
4. Rate severity: Critical / Important / Suggestion
Provide a final verdict: APPROVE, REQUEST CHANGES, or NEEDS DISCUSSION.Codex Code Review
Prerequisites
- Codex CLI installed (
codex --versionto verify) - OpenAI authentication configured (
codex login) - Git repository with changes to review
Available Models
| Model | Use Case | Cost |
|---|---|---|
gpt-5.2-codex | Latest, high reasoning (default) | High |
gpt-5.1-codex-max | Maximum thoroughness | High |
gpt-5.1-codex | Balanced | Medium |
gpt-5.1-codex-mini | Fast reviews | Low |
CLI Execution
codex exec \
-s read-only \
-m gpt-5.2-codex \
-c model_reasoning_effort="xhigh" \
"<review-prompt>"For large diffs, pipe via stdin:
cat <<'EOF' | codex exec -s read-only -m gpt-5.2-codex -c model_reasoning_effort="xhigh" -
<review-prompt-content>
EOFCodex Review Examples
# Basic review (uncommitted changes)
CONTEXT=$(cat CLAUDE.md 2>/dev/null | head -200)
DIFF=$(git diff HEAD)
codex exec -s read-only -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
"Review these changes. Context: $CONTEXT. Diff: $DIFF"
# Review with specific focus
codex exec -s read-only -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
"Review for security vulnerabilities and SQL injection risks only. Diff: $(git diff HEAD)"
# Review against main branch
DIFF=$(git diff main...HEAD)
codex exec -s read-only -m gpt-5.2-codex -c model_reasoning_effort="xhigh" \
"Review all changes on this feature branch. $DIFF"Why codex exec over codex review
| Aspect | codex review | codex exec (recommended) |
|---|---|---|
| Prompt | Codex's opinionated | Custom, project-aware |
| Context | None | CLAUDE.md, lessons |
| Focus | Generic | Explicit guidance |
| Flexibility | Limited | Full control |
Codex Error Handling
| Error | Resolution |
|---|---|
| CLI not found | Install: npm install -g @openai/codex then codex login |
| Auth failed | Run: codex login |
| No changes found | Verify scope: uncommitted, staged, branch, or commit SHA |
| Diff too large | Review specific files, break into smaller commits, or use --staged incrementally |
| Context gathering failed | Proceed with generic review; note that CLAUDE.md/.agents/lessons/ improve results |
Gemini Code Review
Prerequisites
- Gemini CLI installed (
gemini --versionto verify) - Google authentication configured
- Git repository with changes to review
Available Models
| Model | Use Case | Cost |
|---|---|---|
gemini-2.5-flash | Fast reviews | Low |
gemini-2.5-pro | Balanced reasoning | Medium |
gemini-3.0-pro-preview | Latest Gemini 3 Pro (default) | Medium |
Parse model from prompt if specified (e.g., "using flash, review..." or "model: gemini-2.5-pro").
CLI Execution
gemini --sandbox --output-format text --model <model> "<review-prompt-with-diff>"Important flags:
--sandbox- Prevents code modifications--output-format text- Plain text output--model <model>- Model to use (default:gemini-3.0-pro-preview)
Gemini Review Examples
# Review unstaged changes
DIFF=$(git diff)
gemini --sandbox --output-format text \
"Review this code diff for bugs, security issues, and code quality problems. Provide file:line references.
$DIFF"
# Review with focus areas
DIFF=$(git diff --cached)
gemini --sandbox --output-format text "$(cat <<EOF
Review this diff focusing on:
1. SQL injection vulnerabilities
2. N+1 query patterns
3. Missing error handling
4. Breaking API changes
Provide specific file:line references for each issue.
Diff:
$DIFF
EOF
)"
# Review branch changes
DIFF=$(git diff main...HEAD)
gemini --sandbox --output-format text \
"Review this branch diff for production readiness. Check for bugs, security issues, performance problems, and test coverage gaps.
$DIFF"
# Review specific files if diff is too large
DIFF=$(git diff -- app/models/user.rb)
gemini --sandbox --output-format text "Review this diff:
$DIFF"Gemini Error Handling
| Error | Resolution |
|---|---|
| CLI not found | Install and authenticate following official docs |
| No changes found | Verify scope: unstaged, staged, branch |
| Diff too large | Split into smaller chunks, review file-by-file, or summarize large files |
Output Format
## [Codex/Gemini] Code Review Results
**Scope:** [uncommitted / staged / base:main / commit:abc123 / files]
**Model:** [model used] (via [Codex/Gemini] CLI)
### Context Used
- CLAUDE.md: [Yes/No - summary of relevant sections]
- Lessons: [Yes/No - count of lessons applied]
- Focus Areas: [List of focus areas]
### Summary
[High-level assessment]
### Issues Found
#### Critical
- **[Issue]** - `file:line` - [Description and fix suggestion]
#### Important
- **[Issue]** - `file:line` - [Description]
#### Suggestions
- **[Suggestion]** - `file:line` - [Description]
### Verdict
[APPROVE / REQUEST CHANGES / NEEDS DISCUSSION]
### Unique Insights
Issues found that might not be in Claude's review:
- [Insight 1]
- [Insight 2]
### Raw Output
<details>
<summary>Full Review</summary>
[Complete unedited response]
</details>Comparing Results with Claude's Review
When presenting results from external LLMs alongside Claude's review, highlight:
- Consensus - Issues both Claude and the external LLM identified
- External-only - Issues only the external LLM caught (Claude's blind spots)
- Claude-only - Issues only Claude caught (for reference)
- Conflicts - Where Claude and the external LLM disagree
Safety Constraints
- Always use sandbox/read-only mode - No code modifications
- Truncate large diffs - Don't overwhelm with huge diffs
- No secrets in prompts - Scrub sensitive data from diffs if needed
- Verify suggestions - External LLM feedback is one perspective, not authoritative