Design Mode
A visual overlay for the browser: annotate a live UI, describe the change in place, and Claude applies it back to your source code, killing the screenshot-and-paste loop of frontend debugging.
This came straight out of my own frontend pain. Iterating on a UI meant screenshotting the browser, pasting it into the agent, and typing out which element I meant and what was wrong, every single round. It was slow and it broke my focus.
Design Mode collapses that loop: you point at the element on the live page, annotate what you want changed right there, and Claude picks it up and edits your source directly. No screenshots, no describing coordinates, no re-explaining context. It reads like magic the first time it edits the right file from a scribble on the screen.