Open a running local app in Builder’s hosted Design editor as iframe-backed screens on an infinite canvas, one per route, for visual inspection, route-state exploration, and source-backed editing. Unlike a static mockup, “the canvas stays connected to the app’s real routes and the local bridge.”
Most of the skill is host plumbing: never run Design locally, start agent-owned dev servers with AUTH_DISABLED=1, probe each route before placing it (“never leave a dead localhost URL in the canvas” and “never present a sign-in page as the requested screen”), leave servers the agent did not start alone, and go through the MCP App bridge or a page-world WebMCP evaluator.
stage-implement, for UI work: the edit happens in the running app’s source, with the canvas as the way to see and choose it.
See Also
- builder-webmcp — the WebMCP bridge this reuses.
- gstack-design-review — a live-site visual audit, as a review step rather than editing.
- stage-implement — the canonical stage this implements.