Fastify + React vs Next.js 16
Real-world performance comparison based on identical SaaS dashboard implementations.
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 | Fastify + React | Next.js 16 | Winner |
|---|---|---|---|
| TTFB (p50) | 42.95ms | 120.95ms | ◀ |
| TTFB (p95) | 46.06ms | 121.63ms | ◀ |
| LCP (p50) | 70ms | 148ms | ◀ |
| LCP (p95) | 78.2ms | 156ms | ◀ |
| 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 | 99 | 91 | ◀ |
| SEO Score | 92 | 100 | ▶ |
| Accessibility Score | 80 | 88 | ▶ |
| 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 | Fastify + React | Next.js 16 | Winner |
|---|---|---|---|
| Exploration Time | 3580ms | N/A | - |
| Exploration Tokens | 3244 | N/A | - |
| Files Examined | 10 | N/A | - |
| Validation Accuracy | 80% | N/A | - |
| Time Per File | 358ms | N/A | - |
| Tokens Per File | 3060 | N/A | - |
| Efficiency Score | 27.95 | N/A | - |
LLM Understanding (Claude Haiku 4.5)
How efficiently Claude Haiku 4.5 understands the codebase. Based on exploration + validation tests.
| Metric | Fastify + React | Next.js 16 | Winner |
|---|---|---|---|
| Exploration Time | 1869ms | N/A | - |
| Exploration Tokens | 3278 | N/A | - |
| Files Examined | 10 | N/A | - |
| Validation Accuracy | 68% | N/A | - |
| Time Per File | 187ms | N/A | - |
| Tokens Per File | 3061 | N/A | - |
| Efficiency Score | 26.22 | N/A | - |
Build Metrics
| Metric | Fastify + React | Next.js 16 | Winner |
|---|---|---|---|
| Bundle Size (JS) | 283.6KB | 2408.8KB | ◀ |
| Bundle Size (CSS) | 23.1KB | 23.4KB | ◀ |
| Build Time | 0s | 7.1s | ◀ |
| Dependencies | 21 | 18 | ▶ |
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