Pr Review Expert

# PR Review Expert

**Tier:** POWERFUL
**Category:** Engineering
**Domain:** Code Review / Quality Assurance

---

## Overview

Structured, systematic code review for GitHub PRs and GitLab MRs. Goes beyond style nits — this skill
performs blast radius analysis, security scanning, breaking change detection, and test coverage delta
calculation. Produces a reviewer-ready report with a 30+ item checklist and prioritized findings.

---

## Core Capabilities

- **Blast radius analysis** — trace which files, services, and downstream consumers could break
- **Security scan** — SQL injection, XSS, auth bypass, secret exposure, dependency vulns
- **Test coverage delta** — new code vs new tests ratio
- **Breaking change detection** — API contracts, DB schema migrations, config keys
- **Ticket linking** — verify Jira/Linear ticket exists and matches scope
- **Performance impact** — N+1 queries, bundle size regression, memory allocations

---

## When to Use

- Before merging any PR/MR that touches shared libraries, APIs, or DB schema
- When a PR is large (>200 lines changed) and needs structured review
- Onboarding new contributors whose PRs need thorough feedback
- Security-sensitive code paths (auth, payments, PII handling)
- After an incident — review similar PRs proactively

---

## Fetching the Diff

### GitHub (gh CLI)
```bash
# View diff in terminal
gh pr diff <PR_NUMBER>

# Get PR metadata (title, body, labels, linked issues)
gh pr view <PR_NUMBER> --json title,body,labels,assignees,milestone

# List files changed
gh pr diff <PR_NUMBER> --name-only

# Check CI status
gh pr checks <PR_NUMBER>

# Download diff to file for analysis
gh pr diff <PR_NUMBER> > /tmp/pr-<PR_NUMBER>.diff
```

### GitLab (glab CLI)
```bash
# View MR diff
glab mr diff <MR_IID>

# MR details as JSON
glab mr view <MR_IID> --output json

# List changed files
glab mr diff <MR_IID> --name-only

# Download diff
glab mr diff <MR_IID> > /tmp/mr-<MR_IID>.diff
```

---

## Workflow

### Step 1 — Fetch Context

```bash
PR=123
gh pr view $PR --json title,body,labels,milestone,assignees | jq .
gh pr diff $PR --name-only
gh pr diff $PR > /tmp/pr-$PR.diff
```

### Step 2 — Blast Radius Analysis

For each changed file, identify:

1. **Direct dependents** — who imports this file?
```bash
# Find all files importing a changed module
grep -r "from ['\"].*changed-module['\"]" src/ --include="*.ts" -l
grep -r "require(['\"].*changed-module" src/ --include="*.js" -l

# Python
grep -r "from changed_module import\|import changed_module" . --include="*.py" -l
```

2. **Service boundaries** — does this change cross a service?
```bash
# Check if changed files span multiple services (monorepo)
gh pr diff $PR --name-only | cut -d/ -f1-2 | sort -u
```

3. **Shared contracts** — types, interfaces, schemas
```bash
gh pr diff $PR --name-only | grep -E "types/|interfaces/|schemas/|models/"
```

**Blast radius severity:**
- CRITICAL — shared library, DB model, auth middleware, API contract
- HIGH     — service used by >3 others, shared config, env vars
- MEDIUM   — single service internal change, utility function
- LOW      — UI component, test file, docs

### Step 3 — Security Scan

```bash
DIFF=/tmp/pr-$PR.diff

# SQL Injection — raw query string interpolation
grep -n "query\|execute\|raw(" $DIFF | grep -E '\$\{|f"|%s|format\('

# Hardcoded secrets
grep -nE "(password|secret|api_key|token|private_key)\s*=\s*['\"][^'\"]{8,}" $DIFF

# AWS key pattern
grep -nE "AKIA[0-9A-Z]{16}" $DIFF

# JWT secret in code
grep -nE "jwt\.sign\(.*['\"][^'\"]{20,}['\"]" $DIFF

# XSS vectors
grep -n "dangerouslySetInnerHTML\|innerHTML\s*=" $DIFF

# Auth bypass patterns
grep -n "bypass\|skip.*auth\|noauth\|TODO.*auth" $DIFF

# Insecure hash algorithms
grep -nE "md5\(|sha1\(|createHash\(['\"]md5|createHash\(['\"]sha1" $DIFF

# eval /