Show HN: AgnosticUI – A source-first UI library built with Lit (opens in new tab)

I’ve spent the last few years building AgnosticUI. It started as a CSS-first monorepo with logic manually duplicated across framework packages. It turned into a maintenance nightmare.

I recently completed a total rewrite in Lit to align with web standards and unify the core. One major architectural shift was moving to a "Source-First" model. Instead of a black box in node_modules, the UI source lives in your local project workspace.

This makes the components fully visible to LLMs, preventing the hallucinations common when AI tries to guess at hidden library APIs. I wrote a technical post-mortem on Frontend Masters detailing the hurdles of this migration (Shadow DOM a11y, Form Participation, and @lit/react vs React 19): https://frontendmasters.com/blog/post-mortem-rewriting-agnos...