My AI agent just built an app in StackBlitz. It never touched my filesystem.

I wanted to test a theory: if an AI agent has a real browser, does it still need a local development environment? So I pointed it at StackBlitz and said: build something. No terminal access. No filesystem. No git clone . Just a browser window pointing at a web IDE. It built a working app. What it built A Synthwave Pomodoro Timer. Neon glow effects, animated perspective grid, blinking colon, mode switching between Focus / Break / Long Break, session counter, Web Audio notification tones. Not a toy — a real, interactive web app with 7,000 characters of CSS, HTML generation, and timer logic. All written through StackBlitz's Monaco editor, running in a Vite dev server, hot-reloading in the preview pane. The finished Synthwave Pomodoro Timer running inside StackBlitz's preview pane — neon cyan and pink text, 25:00 countdown, animated grid background How it actually worked The agent navigated to stackblitz.com/fork/vite . A fresh Vite project spun up in the browser — editor on the left, term