name: react-router-code-review
description: Reviews React Router code for proper data loading, mutations, error handling, and navigation patterns. Use when reviewing React Router v6.4+ code, loaders, actions, or navigation logic.

React Router Code Review

Quick Reference

Review Checklist

• [ ] Data loaded via loader not useEffect
• [ ] Route params accessed type-safely with validation
• [ ] Using defer() for parallel data fetching when appropriate
• [ ] Mutations use <Form> or useFetcher not manual fetch
• [ ] Actions handle both success and error cases
• [ ] Error boundaries with errorElement on routes
• [ ] Using isRouteErrorResponse() to check error types
• [ ] Navigation uses <Link> over navigate() where possible
• [ ] Pending states shown via useNavigation() or fetcher.state
• [ ] No navigation in render (only in effects or handlers)

Valid Patterns (Do NOT Flag)

These patterns are correct React Router usage - do not report as issues:

• useEffect for client-only data - Loaders run server-side; localStorage, window dimensions, and browser APIs must use useEffect
• navigate() in event handlers - Link is for declarative navigation; navigate() is correct for imperative navigation in callbacks/handlers
• Type annotation on loader data - useLoaderData<typeof loader>() is a type annotation, not a type assertion
• Empty errorElement at route level - Route may intentionally rely on parent error boundary
• Form without action prop - Posts to current URL by convention; explicit action is optional
• loader returning null - Valid when data may not exist; null is a legitimate loader return value
• Using fetcher.data without checking fetcher.state - May be intentional when stale data is acceptable during revalidation

Context-Sensitive Rules

Only flag these issues when the specific context applies:

When to Load References

• Reviewing data fetching code → data-loading.md
• Reviewing forms or mutations → mutations.md
• Reviewing error handling → error-handling.md
• Reviewing navigation logic → navigation.md

Review Questions

1. Is data loaded in loaders instead of effects?
2. Are mutations using Form/action patterns?
3. Are there error boundaries at appropriate route levels?
4. Is navigation declarative with Link components?
5. Are pending states properly handled?

Before Submitting Findings

Load and follow review-verification-protocol before reporting any issue.