hwatu opens a verification browser window in 13ms

hwatu spawns a prewarmed WebKitGTK window in 13 milliseconds, per a July 29 Show HN post. That speed is the point for anyone wiring an agent to check its own UI output. A verification loop that opens in 13 milliseconds can run after every edit. It doesn't have to wait for the end of a task.

That's the median for a focused window; headless spawns land at 14ms. Its check command runs a full headless JavaScript evaluation plus a screenshot in about 35 to 39 milliseconds. hwatu gets there by keeping a WebView warm in a background daemon and handing windows to a client on request. That's the same daemon-client split Emacs uses with emacsclient.

The diff command

The diff command is the sharper piece. It pixel-matches two windows to track how close an agent's output sits to a target. The project's own demo used it to walk a Stripe clone from 85.1% match to 98.8%. That's a way to score whether a UI is done without a person looking at the screen.

Yes, but: it only runs on Linux and Wayland. It's built on WebKit instead of Chromium. Its input events are synthetic JavaScript dispatches, not real OS-level clicks and keystrokes. Anything depending on Chromium-specific rendering, X11, or genuine input timing is out of reach. It's a verification tool for checking rendering, not a general browser automation replacement.