vercel-functions

Create a route handler file like app/api/hello/route.ts and export named functions such as GET or POST that return a Response. Vercel deploys these as Serverless Functions on the Node.js runtime by default.

Use Edge Functions for ultra-low latency tasks like auth checks and redirects, since they cold start in under 1ms but lack full Node.js APIs. Use Serverless Functions when you need npm packages, database connections, or longer execution durations.

Yes, Vercel Functions support bidirectional WebSocket connections on Fluid Compute using libraries like ws or Socket.IO. In Next.js, use experimental_upgradeWebSocket from @vercel/functions inside a route handler.

No, streaming responses and Server-Sent Events work on the default Node.js runtime with Fluid Compute. Staying on Node.js keeps full API access, npm packages, and longer durations.

All plans default to 300s execution with Fluid Compute, extendable to 800s on Pro and Enterprise via maxDuration in vercel.json. For tasks lasting hours, move the logic to the Vercel Workflow SDK for durable execution.

Express middleware, req/res objects, and app.listen() do not work in Vercel's serverless model. Replace Express with Next.js route handlers exporting GET/POST functions that use the Web Request/Response API.