I Built a Browser-Native AI App With No Backend — Here’s What I Learned

Combining Chrome's new WebMCP API with Transformers.js taught me that AI development isn't just a backend problem anymore When most people think about adding AI to a web app, they picture the same architecture: a frontend that sends requests to a backend that calls OpenAI or Anthropic, and a response that travels back the same way. It works. But it also means API bills, latency, data leaving the device, and infrastructure to maintain. I wanted to challenge that assumption. So I built a document analysis app where everything — the AI model, the tool execution, the agent reasoning — runs entirely in the browser. No backend. No API keys. No cloud inference. Two tools made it possible: Transformers.js and Chrome's WebMCP API . They solve different problems, and combining them produced something more interesting than either could alone. Transformers.js: The Model Comes to the Browser Transformers.js is Hugging Face's JavaScript library for running AI models locally in the browser. It uses O