TanStack Start vs Fastify + React
Real-world performance comparison based on identical SaaS dashboard implementations.
TanStack Start
VPS
A full-stack React framework from the creators of TanStack Query, Table, and Router. Built on Vinxi (a Vite-based meta-framework engine), TanStack Start brings the TanStack philosophy of type-safety and developer experience to server rendering. Features isomorphic data fetching with TanStack Router's loader patterns, full-stack type safety from database to component, and first-class support for server functions. The router provides file-based routing with powerful search param management. Still in beta but rapidly maturing, TanStack Start appeals to developers who love TanStack Query's patterns and want them extended to the full stack.
Performance Metrics
Lower is better for all metrics. Green indicates the faster framework.
| Metric | TanStack Start | Fastify + React | Winner |
|---|---|---|---|
| TTFB (p50) | 50ms | 340.9ms | ◀ |
| TTFB (p95) | 55.06ms | 402.72ms | ◀ |
| LCP (p50) | 76ms | 370ms | ◀ |
| LCP (p95) | 84ms | 430.6ms | ◀ |
| 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 | 96 | ◀ |
| SEO Score | 92 | 92 | = |
| Accessibility Score | 86 | 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 | TanStack Start | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 3649ms | N/A | - |
| Exploration Tokens | 3993 | N/A | - |
| Files Examined | 10 | N/A | - |
| Validation Accuracy | 93% | N/A | - |
| Time Per File | 365ms | N/A | - |
| Tokens Per File | 3258 | N/A | - |
| Efficiency Score | 31.16 | N/A | - |
LLM Understanding (Claude Haiku 4.5)
How efficiently Claude Haiku 4.5 understands the codebase. Based on exploration + validation tests.
| Metric | TanStack Start | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 3047ms | N/A | - |
| Exploration Tokens | 4017 | N/A | - |
| Files Examined | 10 | N/A | - |
| Validation Accuracy | 80% | N/A | - |
| Time Per File | 305ms | N/A | - |
| Tokens Per File | 3263 | N/A | - |
| Efficiency Score | 30.79 | N/A | - |
Build Metrics
| Metric | TanStack Start | Fastify + React | Winner |
|---|---|---|---|
| Bundle Size (JS) | 382.4KB | 285.3KB | ▶ |
| Bundle Size (CSS) | 22.8KB | 23.1KB | ◀ |
| Build Time | 0s | 2.5s | ◀ |
| Dependencies | 21 | 21 | = |
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