Code Review

Code Review

Review code for quality issues, code smells, and pragmatic programming violations.

When to Use

Use this skill when the user asks for a code review, PR review, audit, security check, or "review my changes". Trigger on phrases like "review this code", "audit this repo", "check this PR for issues", or "find bugs in these files". Do not trigger for performance profiling, writing new features from scratch, or test-case generation.

Quick Start

First, run the Repo Sync workflow below. Then complete the Environment Check to pick a mode (PR/diff vs full audit). Next, follow the Instructions phases (checklist scan -> findings synthesis -> validation). Finally, emit the Output Format report and verify Acceptance Criteria.

Overview

The skill orchestrates parallel reviewer subagents over batched files, then runs a validator pass. Each phase has explicit steps below. Read only the section you need; the rest is reference material.

Repo Sync Before Edits (mandatory)

Before creating/updating/deleting files in an existing repository, sync the current branch with remote:

branch="$(git rev-parse --abbrev-ref HEAD)"
git fetch origin
git pull --rebase origin "$branch"

If the working tree is not clean, stash first, sync, then restore:

git stash push -u -m "pre-sync"
branch="$(git rev-parse --abbrev-ref HEAD)"
git fetch origin && git pull --rebase origin "$branch"
git stash pop

If origin is missing, pull is unavailable, or rebase/stash conflicts occur, stop and ask the user before continuing.

Environment Check

Before proceeding with code review:

1. Verify Agent tool availability: Check if /Agent subagent system is available
2. Codebase scope: Determine if full audit or PR/diff review
3. Context budget: Estimate file count and total lines to review

• Small PR/diff: 200 files, >50K lines → sample entry points and hot paths

Subagent Architecture

Pattern: B (Parallel Workers) + C (Review Loop)

For full codebase audits and large PRs, use parallel subagent architecture:

┌─────────────────────────────────┐
│  Main SKILL (Orchestrator)      │
│  - Parse scope (PR/audit)       │
│  - Batch files into groups      │
│  - Check Agent availability     │
└──────────────┬──────────────────┘
               │
       ┌───────┴───────┬───────────┬─────────────┐
       │               │           │             │
       v               v           v             v
   ┌────────────┐ ┌────────────┐ ┌────────────┐ ┌────────────┐
   │ Reviewer 1 │ │ Reviewer 2 │ │ Reviewer 3 │ │ Reviewer N │
   │   Batch 1  │ │   Batch 2  │ │   Batch 3  │ │  Batch N   │
   │   5-10     │ │   5-10     │ │   5-10     │ │   5-10     │
   │   files    │ │   files    │ │   files    │ │   files    │
   │ (parallel) │ │ (parallel) │ │ (parallel) │ │ (parallel) │
   └─────┬──────┘ └─────┬──────┘ └─────┬──────┘ └─────┬──────┘
         │              │              │              │
         │              └──────────────┴──────────────┘
         │                             │
         └─────────────────────────────┘
                     │
        ┌────────────v────────────────┐
        │  Report Assembler           │
        │  - Merge all findings       │
        │  - Deduplicate issues       │
        │  - Rank by severity         │
        │  - Generate CODE_REVIEW.md  │
        └────────────┬────────────────┘
                     │
             ┌───────v────────┐
             │  Reviewer      │
             │  Validator     │
             │  - Fresh eyes  │
             │  - Verify      │
             │  - Completeness│
             └────────────────┘

Agent Files

• agents/file-reviewer.md — Review a batch of 5-10 files against the full checklist
• Returns structured JSON with findings, severity levels, and fix suggestions
• Run in parallel on multiple batches
• Input: file list, checklist config, language context
• Output: JSON with findings array

• agents/report-assembler.md — Merge all batch results into one report
• Deduplicates findings by (file, line, smell)
• Ranks by severity (critical → major → minor → info)
• Identifies cross-file patterns (duplicate code, shotgun surgery)
• Generates final CODE_REVIEW.md
• Input: array of JSON outputs from file-reviewer
• Output: Markdown report + validation JSON

• agents/reviewer.md — Fresh-context validation pass
• Verifies accuracy of all findings
• Catches false positives and severity miscategorizations
• Identifies missed issues
• Returns validation report with corrections
• Input: CODE_REVIEW.md + original source files
• Output: Validation JSON + updated CODE_REVIEW.md if corrections needed

Mode Selection & Degradation

Mode 1: Small PR/Diff (Fast Path - Inline)

• Changed files: 200
• Total lines: >50K
• Process:

1. Identify and scan entry points (main, index, app files)
2. Scan business logic hotspots (most frequently modified)
3. Sample distributed files across codebase
4. Use parallel batching as in Mode 2
5. Full validation pass

• Output: CODE_REVIEW.md with sampled findings + note about sampling strategy

Graceful Degradation

If Agent tool unavailable:

• Fall back to inline execution in main SKILL.md
• Use sequential file processing instead of parallel batches
• Return CODE_REVIEW.md without validation pass
• Log message: "Subagent architecture unavailable; running inline review"

Risk Mitigation

Missed cross-file smells: Report-assembler cross-file analysis partially mitigates by identifying:

• Duplicate code patterns
• Shotgun surgery risks
• Architectural coupling

Context overflow: Batching 5-10 files per agent keeps context manageable while maintaining review quality.

False positives: Reviewer agent catches most false positives through fresh-context validation before final report.

Review Modes

Mode 1: PR/Diff Review

# Get changed files
git diff --name-only ..HEAD
git diff ..HEAD

Focus only on changed lines and their immediate context.

Mode 2: Full Codebase Audit

Scan all source files, prioritizing:

1. Entry points (main, index, app)
2. Core business logic
3. Frequently modified files (git log --format='%H' | head -100 | xargs -I{} git diff-tree --no-commit-id --name-only -r {} | sort | uniq -c | sort -rn)

Review Checklist

1. Code Smells (Critical)

Read references/code-smells.md when a code smell is identified that requires the full catalog for classification.

Bloaters - Code that grows too large

• Long Method (>20 lines)
• Large Class (>200 lines)
• Long Parameter List (>3 params)
• Primitive Obsession

Object-Orientation Abusers

• Switch Statements (replace with polymorphism)
• Refused Bequest
• Alternative Classes with Different Interfaces

Change Preventers

• Divergent Change (one class, many reasons to change)
• Shotgun Surgery (one change, many classes affected)
• Parallel Inheritance Hierarchies

Dispensables

• Dead Code
• Duplicate Code
• Lazy Class
• Speculative Generality

Couplers

• Feature Envy
• Inappropriate Intimacy
• Message Chains
• Middle Man

2. Pragmatic Programmer Principles

DRY (Don't Repeat Yourself)

• Duplicated logic or knowledge
• Copy-paste code
• Repeated magic values

Orthogonality

• Components that should be independent but aren't
• Changes rippling across unrelated modules

Reversibility

• Hard-coded decisions that should be configurable
• Vendor lock-in without abstraction

Tracer Bullets

• Is the code testable end-to-end?
• Are there integration points?

Good Enough Software

• Over-engineering for unlikely scenarios
• Premature optimization

Broken Windows

• Commented-out code
• TODO/FIXME without tickets
• Inconsistent formatting

3. Security & Safety

• Input validation
• SQL injection risks
• XSS vulnerabilities
• Hardcoded secrets
• Unsafe deserialization

4. Maintainability

• Unclear naming
• Missing or outdated comments
• Complex conditionals
• Deep nesting (>3 levels)
• Missing error handling

Output Format

Generate CODE_REVIEW.md:

# Code Review Report

**Date**: YYYY-MM-DD
**Scope**: [PR #123 | Full Audit]
**Files Reviewed**: N

## Summary

| Severity | Count |
|----------|-------|
| Critical | X |
| Major    | X |
| Minor    | X |
| Info     | X |

## Critical Issues

### [Category]: Issue Title
**File**: `path/to/file.ts:42`
**Smell**: [Code smell name]

Description of the issue.

**Before**:
```language
// problematic code

Suggested Fix:

// improved code

Major Issues

...

Minor Issues

...

Recommendations

1. Priority fixes
2. Refactoring suggestions
3. Architecture improvements

## Expected Output

A `CODE_REVIEW.md` file with findings grouped by severity. Example:

```markdown
# Code Review Report

**Date**: 2024-01-15
**Scope**: PR #42 — auth module refactor
**Files Reviewed**: 8

## Summary

| Severity | Count |
|----------|-------|
| Critical | 1     |
| Major    | 3     |
| Minor    | 5     |
| Info     | 2     |

## Critical Issues

### [Security]: Hardcoded API Secret
**File**: `src/auth/client.ts:17`
**Smell**: Hardcoded secrets

API key is embedded directly in source code and will be committed to version control.

**Before**:
```typescript
const API_KEY = "sk-prod-abc123xyz";

Suggested Fix:

const API_KEY = process.env.API_KEY;
if (!API_KEY) throw new Error("API_KEY env var is required");

Recommendations

1. Move all secrets to environment variables immediately
2. Add .env to .gitignore and document required vars in README
3. Consider extracting the 240-line UserService class into smaller focused services

## Acceptance Criteria

A run passes when **all** of the following are true:

- [ ] `CODE_REVIEW.md` exists in the repo root with `# Code Review Report` as the first heading.
- [ ] Report includes a `## Summary` table with rows for Critical, Major, Minor, and Info severities.
- [ ] Every reported finding cites a `path/to/file.ext:line` reference and a code smell or category label.
- [ ] Critical findings include both a "Before" and "Suggested Fix" code block when a code change is proposed.
- [ ] Mode used (Mode 1/2/3) is recorded in the report header along with the file count.
- [ ] No merge-conflict markers (`>>>>>>`) are silently dropped — they appear as Critical findings if present in the source.

## Edge Cases

- **Empty or whitespace-only diff**: Report scope as zero files reviewed; skip review and inform the user.
- **Binary files or generated code**: Skip minified/generated files (e.g., `dist/`, `*.min.js`, `package-lock.json`) and note them as excluded in the report header.
- **Single-language vs. polyglot repos**: Apply language-appropriate checks for each file; don't flag Python idioms as issues in JS files.
- **No issues found**: Produce a report with all-zero severity counts and a brief "LGTM" summary — don't fabricate findings.
- **Files exceeding context limits**: Fall back to mode 3 (sampling) and note which files were sampled vs. fully reviewed.
- **Merge conflict markers**: Flag any `>>>>>>` as a Critical issue — never silently ignore them.

## Step Completion Reports

After completing each major step, output a status report in this format:

◆ [Step Name] ([step N of M] — [context]) ·································································· [Check 1]: √ pass [Check 2]: √ pass (note if relevant) [Check 3]: × fail — [reason] [Check 4]: √ pass [Criteria]: √ N/M met ____________________________ Result: PASS | FAIL | PARTIAL

Adapt the check names to match what the step actually validates. Use `√` for pass, `×` for fail, and `—` to add brief context. The "Criteria" line summarizes how many acceptance criteria were met. The "Result" line gives the overall verdict.

### Skill-specific checks per phase

**Phase: Scope Assessment** — checks: `Scope assessment`, `File count estimated`

**Phase: Review Execution** — checks: `Code smell detection`, `Security scan`

**Phase: Report Generation** — checks: `Report generation`, `Severity classification`

**Phase: Validation Pass** — checks: `Validation pass`, `False positive check`

## Severity Levels

| Level | Description | Action |
|-------|-------------|--------|
| **Critical** | Security risks, bugs, data loss potential | Must fix before merge |
| **Major** | Code smells, maintainability blockers | Should fix soon |
| **Minor** | Style, minor improvements | Nice to have |
| **Info** | Suggestions, alternatives | Optional |

## Resources

- [references/code-smells.md](references/code-smells.md) - Complete catalog of code smells with examples

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [luongnv89](https://github.com/luongnv89)
- **Source:** [luongnv89/skills](https://github.com/luongnv89/skills)
- **License:** MIT
- **Homepage:** https://luongnv.com

Install and usage instructions live in the source repository linked above.