Proto is a Y Combinator Fall 2026 company building an IDE for product designers who are already working inside coding agents. It follows the agent workflow of Cursor and Claude Code, then adds the design controls those tools leave out, including rapid visual variants, a state map of a prototype's layers, and a state machine that fills in loading, empty, and error states. Comments snapshot the selected component, so a note can reload the exact screen it was written on. A limited early access pilot is open at prototypes.fun. Founder Maayan Albert has spent a decade on creative tools, including an IDE for p5 as a Carnegie Mellon senior thesis, and previously worked at Browserbase, Apple, and Google. On the YC launch, Albert said design tools have not kept up with AI workflows, which pushed designers into developer IDEs, and that Proto was built with a co-founder to put the missing design features in one place. The San Francisco company opened signups with a public launch video.