I Built a ChatGPT-Clone in 100 Lines of Next.js (Streaming + Tools + One-Line Provider Swap)

Open ai-sdk-from-zero.vercel.app. Type "what time is it in Tokyo?"

Watch the tokens stream in. A small 🔧 get_current_time pill appears mid-message. Then the assistant tells you the actual time, in actual Tokyo, computed by an actual function I wrote — not made up from training data.

That's three years of "this is hard" disappearing in ~100 lines of Next.js.

What the Vercel AI SDK fixes

Three years ago, "stream LLM tokens to a browser" meant standing up a WebSocket server, hand-decoding SSE frames, and writing a careful state machine to append text to a React ref without dropping frames or double-rendering on StrictMode.