Elysia + React vs Fastify + React
Real-world performance comparison based on identical SaaS dashboard implementations.
Elysia + React
VPS (Bun)
A Bun-native server framework paired with React for SSR. Elysia leverages Bun's speed and provides end-to-end type safety through its innovative "Eden" client that infers types directly from your API routes. Elysia's declarative syntax is reminiscent of tRPC but with full HTTP control. Plugins handle validation, authentication, and documentation generation. The framework achieves exceptional throughput on the Bun runtime. This stack demonstrates what's possible when you combine Bun's performance with a thoughtfully designed type-safe server framework and React's component model.
Performance Metrics
Lower is better for all metrics. Green indicates the faster framework.
| Metric | Elysia + React | Fastify + React | Winner |
|---|---|---|---|
| TTFB (p50) | 44.75ms | 340.9ms | ◀ |
| TTFB (p95) | 50.52ms | 402.72ms | ◀ |
| LCP (p50) | 72ms | 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 | 100 | 96 | ◀ |
| SEO Score | 92 | 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 | Elysia + React | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 3484ms | N/A | - |
| Exploration Tokens | 3402 | N/A | - |
| Files Examined | 10 | N/A | - |
| Validation Accuracy | 74% | N/A | - |
| Time Per File | 348ms | N/A | - |
| Tokens Per File | 3070 | N/A | - |
| Efficiency Score | 23.18 | N/A | - |
LLM Understanding (Claude Haiku 4.5)
How efficiently Claude Haiku 4.5 understands the codebase. Based on exploration + validation tests.
| Metric | Elysia + React | Fastify + React | Winner |
|---|---|---|---|
| Exploration Time | 2400ms | N/A | - |
| Exploration Tokens | 3430 | N/A | - |
| Files Examined | 10 | N/A | - |
| Validation Accuracy | 63% | N/A | - |
| Time Per File | 240ms | N/A | - |
| Tokens Per File | 3060 | N/A | - |
| Efficiency Score | 15.01 | N/A | - |
Build Metrics
| Metric | Elysia + React | Fastify + React | Winner |
|---|---|---|---|
| Bundle Size (JS) | 283.6KB | 285.3KB | ◀ |
| Bundle Size (CSS) | 23.1KB | 23.1KB | = |
| Build Time | 0s | 2.5s | ◀ |
| Dependencies | 20 | 21 | ◀ |
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