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

1. Determine review scope (uncommitted, staged, branch, specific commit)
2. Gather the diff and project context (CLAUDE.md, lessons)
3. Build a review prompt with context, focus areas, and the diff
4. Execute the external CLI in sandbox/read-only mode
5. 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.rb

Gathering 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/*.md

Lessons 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 --version to 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>
EOF

Codex 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 --version to 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:

1. Consensus - Issues both Claude and the external LLM identified
2. External-only - Issues only the external LLM caught (Claude's blind spots)
3. Claude-only - Issues only Claude caught (for reference)
4. 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