How to Use Claude for Code Review: A Practical Developer's Guide

Code review is one of the highest-leverage activities in software development — and one of the most consistently under-resourced. Reviewers miss bugs because they're tired, skip security checks because they're rushed, and leave style feedback that wastes everyone's time arguing about tabs.

Claude changes the economics of code review. You can get a thorough first-pass review in seconds, catch security issues that exhausted humans miss, and focus human reviewers on architecture and intent — the things that actually require judgment.

This guide covers three ways to use Claude for code review: interactive review in Claude Code, automated PR review via GitHub Actions, and targeted review with custom prompts. Pick the one that matches where you are today.

Why Claude Works Well for Code Review

Before getting into setup, it helps to understand where Claude adds the most value — and where it doesn't.

• Security vulnerability detection — SQL injection, XSS, insecure deserialization, hardcoded secrets, OWASP Top 10 patterns. Claude has seen more vulnerable code than any individual engineer and recognizes patterns instantly.
• Logic errors and edge cases — Off-by-one bugs, null pointer conditions, race conditions, incorrect boundary checks. These are exactly the bugs that tired reviewers miss at 5pm.
• Consistency with existing patterns — When you give Claude the codebase context (via CLAUDE.md or a system prompt), it flags code that violates your team's conventions.
• Documentation gaps — Missing function docs, unclear variable names, under-specified error handling.
• Dependency and import analysis — Unused imports, circular dependencies, overly broad package inclusions.

• Business logic correctness — Claude can't tell if your pricing calculation is right without your business rules. It can tell you the code does what it says, but not whether it does what you need.
• Performance at scale — Static review doesn't substitute for profiling. Claude can flag obvious O(n²) loops but won't catch that your query pattern degrades at 10M rows.
• Architectural decisions — Whether microservices vs monolith is right for your org involves context Claude doesn't have unless you tell it.

The right mental model: Claude is a brilliant, tireless junior reviewer who catches implementation mistakes at scale. Pair it with human reviewers who evaluate intent and architecture.

Method 1: Interactive Code Review with Claude Code

If you already use Claude Code, this is the lowest-friction starting point. Claude Code can review files, diffs, or entire PRs from your terminal.

Basic File Review

The simplest workflow — pass a file to Claude and ask for a review:

bashclaude "Review src/api/payments.ts for security issues, logic errors, 
and anything that violates our patterns in CLAUDE.md"

Claude reads the file, applies any context from your CLAUDE.md, and returns structured feedback. For more structured output, add formatting instructions:

bashclaude "Review src/api/payments.ts. Format your response as:
## Critical (must fix before merge)
## Warnings (should fix)  
## Suggestions (optional improvements)
## Looks good (what you verified is correct)"

Reviewing a Git Diff

More useful in practice: review only what changed in a PR.

bash# Review staged changes
git diff --cached | claude "Review these changes. Flag bugs, security issues, 
and violations of our conventions."

# Review changes on a feature branch vs main
git diff main...feature/new-auth | claude "Code review. Be specific — 
include file names and line numbers in your feedback."

Using Claude Code's Built-in /review Command

Claude Code ships with a /review command that uses subagents to perform multi-dimensional analysis. Run it from within a Claude Code session:

/review

This triggers a review of the current diff with structured output covering correctness, security, performance, and style. You can extend it by adding review instructions to your CLAUDE.md:

markdown## Code Review Standards (for /review command)
- Always check for SQL injection in any database query
- Flag any function longer than 50 lines
- Verify error responses never leak stack traces
- Check that all API endpoints have authentication middleware

With these in place, /review automatically applies your team's standards on every run.

Method 2: Automated PR Review via GitHub Actions

The most scalable approach: wire Claude into your CI/CD pipeline so every PR gets an automatic review before a human looks at it.

Prerequisites

• A GitHub repository
• An Anthropic API key (stored as ANTHROPIC_API_KEY in GitHub Secrets)

Step 1: Create the Review Script

Create scripts/claude-review.mjs in your repo:

javascriptimport Anthropic from "@anthropic-ai/sdk";
import { spawnSync } from "child_process";
import fs from "fs";

const client = new Anthropic();

function getDiff() {
  // Use spawnSync (safer than exec — no shell interpolation)
  const result = spawnSync(
    "git",
    ["diff", "origin/main...HEAD", "--unified=5"],
    { encoding: "utf-8" }
  );
  if (result.status !== 0) {
    throw new Error(`git diff failed: ${result.stderr}`);
  }
  return result.stdout;
}

async function reviewPR() {
  const diff = getDiff();

  if (!diff.trim()) {
    console.log("No changes to review.");
    process.exit(0);
  }

  // Optionally load project context
  let projectContext = "";
  if (fs.existsSync("CLAUDE.md")) {
    projectContext = fs.readFileSync("CLAUDE.md", "utf-8");
  }

  const systemPrompt = `You are a senior software engineer performing a thorough code review.
${projectContext ? `\n## Project Context\n${projectContext}` : ""}

Your review should:
1. Check for security vulnerabilities (XSS, SQL injection, auth bypasses, secrets in code)
2. Identify logic bugs and edge cases
3. Flag missing error handling
4. Note performance concerns
5. Check for incomplete or misleading documentation

Format your response with these exact sections:
## 🔴 Critical Issues (block merge)
## 🟡 Warnings (fix recommended)
## 🔵 Suggestions (optional)
## ✅ Verified Correct

If a section is empty, write "None found." Keep feedback specific — include file names and line numbers.`;

  const message = await client.messages.create({
    model: "claude-opus-4-6",
    max_tokens: 4096,
    system: systemPrompt,
    messages: [
      {
        role: "user",
        content: `Please review this pull request diff:\n\n\`\`\`diff\n${diff}\n\`\`\``,
      },
    ],
  });

  const review = message.content[0].text;
  console.log(review);

  // Write to a file for the GitHub Actions step to use
  fs.writeFileSync("review-output.md", review);
}

reviewPR().catch((err) => {
  console.error("Review failed:", err.message);
  process.exit(1);
});

Step 2: Create the GitHub Actions Workflow

Create .github/workflows/claude-review.yml:

yamlname: Claude Code Review

on:
  pull_request:
    types: [opened, synchronize]

permissions:
  pull-requests: write
  contents: read

jobs:
  review:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - uses: actions/setup-node@v4
        with:
          node-version: "20"

      - name: Install dependencies
        run: npm install @anthropic-ai/sdk

      - name: Run Claude review
        env:
          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
        run: node scripts/claude-review.mjs

      - name: Post review as PR comment
        uses: actions/github-script@v7
        with:
          script: |
            const fs = require('fs');
            const review = fs.readFileSync('review-output.md', 'utf8');
            
            await github.rest.issues.createComment({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              body: `## 🤖 Claude Code Review\n\n${review}\n\n---\n*Automated review by Claude. Human review still required for architecture and business logic.*`
            });

Once deployed, every PR automatically gets a Claude review comment within 30-60 seconds of opening. Human reviewers arrive to a pre-triaged diff with the obvious issues already flagged.

Controlling Cost

Claude Opus 4.6 costs ~$15/million input tokens. A typical 200-line diff is around 3,000 tokens — roughly $0.05 per review. For a team doing 20 PRs/day, that's about $1/day. For large monorepo diffs, use --diff-filter=M to only review modified files:

bashgit diff origin/main...HEAD --diff-filter=M --unified=5

You can also route model selection by PR sensitivity:

javascript// Use Opus for security-sensitive paths, Sonnet for routine changes
const isSensitive =
  diff.includes("auth") ||
  diff.includes("payment") ||
  diff.includes("crypto");
const model = isSensitive ? "claude-opus-4-6" : "claude-sonnet-4-6";

Method 3: Targeted Review with Custom Prompts

Sometimes you don't want a full review — you want a targeted analysis. These prompts are designed for specific scenarios.

Security-Only Review

Review this code for security vulnerabilities only. For each finding:
- Vulnerability type (e.g., SQL injection, XSS, path traversal)
- Severity (Critical/High/Medium/Low)
- Specific line(s) affected
- Why it's exploitable
- Exact fix with code example

Do not comment on style, naming, or non-security issues.

[paste code here]

Performance Review

Review this code for performance issues. Focus on:
- Time complexity (identify O(n²) or worse loops)
- Unnecessary database queries in loops (N+1 problem)
- Memory leaks or unbounded growth
- Synchronous operations that should be async
- Missing indexes implied by query patterns

For each issue, estimate the impact at scale (1K users vs 1M users).

[paste code here]

Review Against a Style Guide

Review this code against our team's style guide:

STYLE RULES:
- Functions must be under 30 lines
- No nested ternaries
- All async functions must have try/catch or .catch()
- Database queries go through the repository layer, never directly in controllers
- Error responses must use our ApiError class, not raw throw

Flag every violation with the rule it breaks. Don't flag anything else.

[paste code here]

"What Could Go Wrong" Analysis

This prompt is particularly effective before shipping critical code:

You are a malicious user and a production incident investigator simultaneously.

For this code:
1. As the attacker: What are 3 ways to exploit or abuse this?
2. As the investigator: What are the top 3 ways this fails under load or at scale?
3. What's the one change that would prevent the worst-case scenario?

[paste code here]

Building a Code Review Workflow for Your Team

Running ad-hoc Claude reviews is useful. Building a system is better. Here's a workflow that combines the approaches above:

Every PR gets a Claude review comment automatically. This catches the 80% — syntax errors, obvious security issues, missing error handling.

Before requesting human review, the author pastes their own diff into Claude with a security-only or logic-check prompt. This catches issues the automated review missed due to context limitations.

With Claude's review already visible, human reviewers skip the line-by-line scan and focus on: Does this solve the right problem? Is the abstraction correct? Does it fit the overall system?

If a bug escapes to production, run Claude over the relevant diff retroactively:

This code was shipped and caused [describe incident]. 
Reviewing it now — what signals should have caught this in review?
Use this to improve our review checklist.

Claude will identify the patterns that should have been caught and give you a concrete addition to your review standards.

Configuring CLAUDE.md for Consistent Reviews

If you use Claude Code, your CLAUDE.md is the most powerful lever for improving review quality. Add a review section:

markdown## Code Review Standards

When reviewing code (via /review or explicit review requests):

### Automatic checks (always perform)
- [ ] No secrets, API keys, or credentials in code
- [ ] All user inputs validated before use in queries/commands
- [ ] Error responses don't expose stack traces or internal paths
- [ ] Authentication checked before authorization in every route handler
- [ ] Database queries use parameterized statements, not string concatenation

### Project-specific patterns
- Repository layer: all DB access through `src/repositories/`, never direct in controllers
- Error handling: use `AppError` class from `src/lib/errors.ts`
- API responses: always use `ApiResponse` wrapper from `src/lib/response.ts`
- Logging: use `logger` from `src/lib/logger.ts`, never `console.log` in production code

### Review format
Always output: Critical → Warnings → Suggestions → Verified Correct
Include file path and line number for every finding.

With this in CLAUDE.md, every review automatically applies your team's specific standards — not just generic best practices.

Key Takeaways

• Claude catches implementation bugs (security, logic, edge cases) extremely well — use it for the first-pass review that humans consistently skip or rush
• GitHub Actions integration turns every PR into an automatically reviewed artifact in under 60 seconds
• The right model split: Claude Opus 4.6 for security-sensitive paths, Claude Sonnet 4.6 for routine changes
• CLAUDE.md review standards make reviews consistent across the whole team without extra process
• Claude doesn't replace human review for architecture and business logic — it frees humans to focus on exactly those things
• Typical cost: $0.03-0.10 per PR review, making it trivially cheap to review every single change

Next Steps

If you're starting with Claude Code, the getting started guide covers the full setup from scratch. For teams who want to go deeper on CI/CD automation, the Claude Code hooks tutorial covers deterministic guardrails that run alongside your review workflow.

Serious about Claude development? The Claude Certified Architect (CCA) certification covers multi-agent workflows, tool use, and agentic patterns — exactly the skills you need to build production-grade automation like the PR review system above. Our CCA exam guide breaks down the full syllabus, and our CCA practice test bank has 200+ exam-style questions with detailed explanations to get you ready faster.