Code Review Router Skill for Codex

Code Review Router

Routes code reviews to the optimal CLI (Gemini or Codex) based on change characteristics.

When NOT to Use This Skill

• For non-code reviews (documentation proofreading, prose editing)
• When reviewing external/third-party code you don't control
• For commit message generation (use a dedicated commit skill)
• When you need a specific reviewer (use that CLI directly)

Step 0: Environment Check

Verify we're in a git repository:

git rev-parse --git-dir 2>/dev/null || echo "NOT_A_GIT_REPO"

If not a git repo: Stop and inform the user: "This directory is not a git repository. Initialize with git init or navigate to a repo."

Step 1: Prerequisites Check

Verify both CLIs are available:

# Check for Gemini CLI
which gemini || echo "GEMINI_NOT_FOUND"

# Check for Codex CLI
which codex || echo "CODEX_NOT_FOUND"

If neither CLI is found: Stop and inform the user they need to install at least one:

• Gemini: Check Google's Gemini CLI installation docs
• Codex: Check OpenAI's Codex CLI installation docs

If only one CLI is available: Use that CLI (no routing needed).

If both are available: Proceed with routing analysis.

Step 2: Analyze Git Diff

Run these commands to gather diff statistics:

# Get diff stats (staged + unstaged)
git --no-pager diff --stat HEAD 2>/dev/null || git --no-pager diff --stat

# Get full diff for pattern analysis
git --no-pager diff HEAD 2>/dev/null || git --no-pager diff

# Count changed files
git --no-pager diff --name-only HEAD 2>/dev/null | wc -l

# Count total changed lines
git --no-pager diff --numstat HEAD 2>/dev/null | awk '{added+=$1; removed+=$2} END {print added+removed}'

If no changes detected: Report "Nothing to review - no uncommitted changes found." and stop.

Step 3: Calculate Complexity Score

Initialize complexity_score = 0, then add points:

| Condition | Points | Detection Method |

|-----------|--------|------------------|

| Files changed > 10 | +2 | git diff --name-only \| wc -l |

| Files changed > 20 | +3 | (additional, total +5) |

| Lines changed > 300 | +2 | git diff --numstat sum |

| Lines changed > 500 | +3 | (additional, total +5) |

| Multiple directories touched | +1 | Count unique dirs in changed files |

| Test files included | +1 | Files matching *test*, *spec* |

| Config files changed | +1 | Files: *.config.*, *.json, *.yaml, *.yml, *.toml |

| Database/schema changes | +2 | Files: *migration*, *schema*, *.sql, prisma/* |

| API route changes | +2 | Files in api/, routes/, containing endpoint, handler |

| Service layer changes | +2 | Files in services/, *service*, *provider* |

Step 4: Detect Language & Framework

Analyze file extensions and content patterns:

Primary Language Detection

.ts, .tsx     → TypeScript
.js, .jsx     → JavaScript
.py           → Python
.go           → Go
.rs           → Rust
.java         → Java
.rb           → Ruby
.php          → PHP
.cs           → C#
.swift        → Swift
.kt           → Kotlin

Framework Detection (check imports/file patterns)

React/Next.js    → "import React", "from 'react'", "next.config", pages/, app/
Vue              → ".vue" files, "import Vue", "from 'vue'"
Angular          → "angular.json", "@angular/core"
Django           → "django", "models.py", "views.py", "urls.py"
FastAPI          → "from fastapi", "FastAPI("
Express          → "express()", "from 'express'"
NestJS           → "@nestjs/", "*.module.ts", "*.controller.ts"
Rails            → "Gemfile" with rails, app/controllers/
Spring           → "springframework", "@RestController"

Security-Sensitive Patterns

Detect by file path OR code content:

File paths:

**/auth/**
**/security/**
**/*authentication*
**/*authorization*
**/middleware/auth*

Code patterns (in diff content):

password\s*=
api_key\s*=
secret\s*=
Bearer\s+
JWT
\.env
credentials
private_key
access_token

Config files:

.env*
*credentials*
*secrets*
*.pem
*.key

Step 5: Apply Routing Decision Tree

Routing Priority Order (evaluate top-to-bottom, first match wins):

Priority 1: Pattern-Based Rules (Hard Rules)

| Pattern | Route | Reason |

|---------|-------|--------|

| Security-sensitive files/code detected | Codex | Requires careful security analysis |

| Files > 20 OR lines > 500 | Codex | Large changeset needs thorough review |

| Database migrations or schema changes | Codex | Architectural risk |

| API/service layer modifications | Codex | Backend architectural changes |

| Changes span 3+ top-level directories | Codex | Multi-service impact |

| Complex TypeScript (generics, type utilities) | Codex | Type system complexity |

| Pure frontend only (jsx/tsx/vue/css/html) | Gemini | Simpler, visual-focused review |

| Python ecosystem (py, Django, FastAPI) | Gemini | Strong Python support |

| Documentation only (md/txt/rst) | Gemini | Simple text review |

Priority 2: Complexity Score (if no pattern matched)

| Score | Route | Reason |

|-------|-------|--------|

| ≥ 6 | Codex | High complexity warrants deeper analysis |

| < 6 | Gemini | Moderate complexity, prefer speed |

Priority 3: Default

→ Gemini (faster feedback loop for unclear cases)

Step 6: Execute Review

Explain Routing Decision

Before executing, output:

## Code Review Routing

**Changes detected:**
- Files: [X] files changed
- Lines: [Y] lines modified
- Primary language: [language]
- Framework: [framework or "none detected"]

**Complexity score:** [N]/10
- [List contributing factors]

**Routing decision:** [Gemini/Codex]
- Reason: [primary reason for choice]

**Executing review...**

CLI Commands

> Note: Gemini receives the diff via stdin (piped), while Codex has a dedicated review subcommand that reads the git context directly. If debugging, check that git diff HEAD produces output before running Gemini.

For Gemini:

# Pipe diff to Gemini with review prompt
git --no-pager diff HEAD | gemini -p "Review this code diff for: 1) Code quality issues, 2) Best practices violations, 3) Potential bugs, 4) Security concerns, 5) Performance issues. Provide specific, actionable feedback."

For Codex:

# Use dedicated 'review' subcommand for non-interactive code review
# Note: --uncommitted and [PROMPT] are mutually exclusive
codex review --uncommitted

Step 7: Handle Failures with Fallback

If the chosen CLI fails (non-zero exit or error output):

• Report the failure:

   [Primary CLI] failed: [error message]
   Attempting fallback to [other CLI]...

• Try the alternative CLI

• If fallback also fails:

   Both review CLIs failed.
   - Gemini error: [error]
   - Codex error: [error]

   Please check CLI installations and try manually.

Step 8: Format Output

Present the review results clearly:

## Code Review Results

**Reviewed by:** [Gemini/Codex]
**Routing:** [brief reason]

---

[CLI output here]

---

**Review complete.** [X files, Y lines analyzed]

Quick Reference

| Change Type | Route | Reason |

|-------------|-------|--------|

| React component styling | Gemini | Pure frontend |

| Django view update | Gemini | Python ecosystem |

| Single bug fix < 50 lines | Gemini | Simple change |

| New API endpoint + tests | Codex | Architectural |

| Auth system changes | Codex | Security-sensitive |

| Database migration | Codex | Schema change |

| Multi-service refactor | Codex | High complexity |

| TypeScript type overhaul | Codex | Complex types |