ui_catalog library

The catalog page: a browsable index of your previews.

What this is for, stated plainly, because it changed. UICatalog is what fw run previews build-web mounts — it is the page's shell, and that is the supported way to reach it. Mounting it yourself still works and is still tested, but nothing is designed around it any more: the generated page is discovered from @Preview annotations, where the widget takes a hand-written map, and the map is the older half of the same tool.

Not the Previews tool. That is previews.dart and the Previews plugin — a panel, a CLI and an MCP surface driving a guest engine. Previews is where you work; this is what you publish for people who are not going to run the tool.

It hosts the same previews. UICatalog renders whatever the scan found, knobs and all, which is why Knobs is re-exported here, with the PickerStyle its pickers take — context.knobs reads the same on a catalog page as in a preview, because it is the same thing being read. A PreviewShell's axes are drawn too, so a page published to be read in a second language can actually be switched into one.