React Router v7 vs Fastify + React
Real-world performance comparison based on identical SaaS dashboard implementations.
React Router v7
VPS
The official React routing library, now evolved into a full-stack framework. React Router v7 represents the merger with Remix, bringing data loading patterns that eliminate waterfalls and keep your UI in sync with your URLs. Loaders fetch data before rendering, actions handle mutations, and the router manages pending/optimistic states automatically. Nested routes enable parallel data loading and isolated error boundaries. Type-safe links catch broken routes at build time. Compared to Next.js, React Router offers a more explicit data flow with loaders/actions and tighter Remix-style conventions. It's particularly strong for apps with complex forms and frequent user interactions.
Fastify + React
VPS
Node.js high-performance web framework combined with React SSR. Fastify is one of the fastest Node.js frameworks, built on a robust plugin architecture with JSON Schema validation and automatic OpenAPI documentation. This implementation uses Fastify as the server with custom React SSR integration. Fastify's encapsulation model keeps plugins isolated, while hooks provide fine-grained request lifecycle control. Ideal for teams with existing Node.js/Express experience who want better performance and structure. Fastify's plugin ecosystem covers everything from rate limiting to WebSocket support.
Performance Metrics
Lower is better for all metrics. Green indicates the faster framework.
| Metric | React Router v7 | Fastify + React | Winner |
|---|---|---|---|
| TTFB (p50) | 50.2ms | 42.95ms | ▶ |
| TTFB (p95) | 51.55ms | 46.06ms | ▶ |
| LCP (p50) | 80ms | 70ms | ▶ |
| LCP (p95) | 86.2ms | 78.2ms | ▶ |
| CLS | 0 | 0 | = |
| TBT | 0 ms | 0 ms | = |
| LCP → TTFB | N/A | N/A | - |
| LCP → Load Delay | N/A | N/A | - |
| LCP → Load Duration | N/A | N/A | - |
| LCP → Render Delay | N/A | N/A | - |
| Performance Score | 98 | 99 | ▶ |
| SEO Score | 83 | 92 | ▶ |
| Accessibility Score | 80 | 80 | = |
| Best Practices Score | 100 | 100 | = |
LLM Understanding (Claude Opus 4.5)
How efficiently Claude Opus 4.5 understands the codebase. Based on exploration + validation tests.
| Metric | React Router v7 | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 3232ms | 3580ms | ◀ |
| Exploration Tokens | 2623 | 3244 | ◀ |
| Files Examined | 8 | 10 | ◀ |
| Validation Accuracy | 73% | 80% | ▶ |
| Time Per File | 404ms | 358ms | ▶ |
| Tokens Per File | 2954 | 3060 | ◀ |
| Efficiency Score | 25.65 | 27.95 | ▶ |
LLM Understanding (Claude Haiku 4.5)
How efficiently Claude Haiku 4.5 understands the codebase. Based on exploration + validation tests.
| Metric | React Router v7 | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 3285ms | 1869ms | ▶ |
| Exploration Tokens | 2751 | 3278 | ◀ |
| Files Examined | 8 | 10 | ◀ |
| Validation Accuracy | 67% | 68% | ▶ |
| Time Per File | 411ms | 187ms | ▶ |
| Tokens Per File | 2969 | 3061 | ◀ |
| Efficiency Score | 19.22 | 26.22 | ▶ |
Build Metrics
| Metric | React Router v7 | Fastify + React | Winner |
|---|---|---|---|
| Bundle Size (JS) | 462.3KB | 283.6KB | ▶ |
| Bundle Size (CSS) | 23.3KB | 23.1KB | ▶ |
| Build Time | 0s | 0s | = |
| Dependencies | 22 | 21 | ▶ |
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