Why I stopped using Vite's default dev server for API development

I used to run my entire development stack through Vite's dev server. Frontend assets served lightning fast, API requests proxied to my backend through Vite's proxy configuration -- it felt like the perfect unified development experience. One command started everything, hot reload worked flawlessly for frontend changes, and the proxy configuration seemed elegant compared to CORS headaches. Most Vite tutorials showed this pattern, and it worked great for simple CRUD apps. Then I built a file upload service where API requests needed custom headers, authentication middleware, and streaming responses.

The breaking point came when I spent three hours debugging a file upload that worked perfectly in production but failed mysteriously in development. The issue was not my code -- Vite's proxy was silently modifying request headers and buffering the entire file stream before forwarding it to my backend. My 100MB video upload would hang for minutes in development while Vite collected the entire stream in memory, but the same upload completed in seconds when hitting the API directly. The proxy configuration looked innocent enough, but it was fundamentally changing how requests behaved.

Here's what my problematic setup looked like:

// vite.config.ts
export default defineConfig({
  server: {
    proxy: {
      '/api': {
        target: 'http://localhost:3001',
        changeOrigin: true,
        secure: false
      }
    }
  }
})

This configuration hides several problems that become obvious under load. First, streaming requests get buffered. Vite collects the entire request body before forwarding it, turning streaming uploads into memory-intensive operations. Second, request timing becomes unpredictable. The proxy adds variable latency that does not exist in production, making performance testing useless. Third, error handling gets obscured. When the backend returns a 500 error, Vite's proxy might transform it into a generic network error, hiding crucial debugging information.

The final straw was authentication debugging. My API used custom headers for JWT token refresh, and certain endpoints required specific Content-Type values for security. In development, requests would fail with vague "unauthorized" errors. In production, the same requests worked perfectly. I'd waste hours debugging my authentication logic when the real issue was Vite's proxy normalizing or dropping headers that my security middleware expected.

Now I run my API server independently and configure my frontend to hit it directly:

// vite.config.ts
export default defineConfig({
  define: {
    __API_URL__: JSON.stringify(process.env.NODE_ENV === 'development' 
      ? 'http://localhost:3001' 
      : 'https://api.myapp.com'
    )
  }
})

// api/client.ts
const API_BASE = __API_URL__;
 
export async function uploadFile(file: File): Promise<UploadResponse> {
  const formData = new FormData();
  formData.append('file', file);
  
  const response = await fetch(`${API_BASE}/api/upload`, {
    method: 'POST',
    body: formData,
    headers: {
      'Authorization': `Bearer ${getToken()}`
    }
  });
  
  if (response.status === 401) {
    await refreshToken();
    // Retry logic here
  }
  
  return response.json();
}

This approach requires handling CORS properly in development, but that's actually beneficial. CORS configuration that works in development will work in production. With Vite's proxy, I was bypassing CORS entirely, which meant CORS issues only surfaced during deployment.

Here's my backend CORS setup for development:

// server.ts
app.use(cors({
  origin: process.env.NODE_ENV === 'development' 
    ? 'http://localhost:5173'  // Vite's default port
    : ['https://myapp.com', 'https://www.myapp.com'],
  credentials: true,
  exposedHeaders: ['X-Total-Count', 'X-Rate-Limit']
}));

The benefits became obvious immediately:

• Real request behavior: Streaming uploads work exactly like production
• Accurate performance testing: No proxy latency masking real API performance
• Better error visibility: Backend errors surface with full details
• CORS validation: Catch cross-origin issues before deployment
• Independent scaling: Frontend and backend can restart independently

The development workflow is slightly more complex -- I need to start both servers -- but that complexity pays off in debugging accuracy. When something breaks in development, I can trust that it's a real issue, not a proxy artifact.

For teams already using Docker or docker-compose, this change is even easier. Just remove the Vite proxy configuration and let each service run on its designated port. Your development environment becomes a more accurate representation of production, and debugging becomes significantly more reliable.

The extra step of managing two processes is worth avoiding the hidden complexity of request proxying through a build tool that was never designed to handle complex API scenarios.