Persona.js
a vanilla-JS agent UI library with native WebMCP (MIT)
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Hey everyone. My cofounder and I are open sourcing Persona.js (https://www.persona-chat.dev/). It's a VanillaJS library that helps anyone build agentic experiences on the web, without a framework dependency, and full WebMCP supportSo, why'd we do this?1) We're super fans of the web and the browser can do a ton today2) We've seen AI builds be way overly complex because the FE requires a large project within an existing app OR the site wasn't using a framework to begin withIf you've been a part of huge apps with multiple frameworks inside them, or work inside CMS / website builders / ecomm platforms... you know what we're talking about. A "simple" AI feature disrupts your life for monthsIf you have a singular React codebase and can't possibly imagine building an interface without JSX, nothing to see here! You already have a lot of great options that are really cool too. Check out Assistant UI / CopilotKit / AI Elements which are all MIT.There's a demo video here: https://www.youtube.com/watch?v=68D80uNsfH0.Some specifics:Persona has a ~15 kB brotli to first paint (the full widget lazy-loads on first click) while being able to render most of the primary agent experiences you see on the web: from 'Fin' (pill launcher) to 'Claude' (fullscreen assistant) to 'Shopify Sidekick' (docked)You can run it in Shadow DOM isolated mode so existing styles play niceEverything has hooks and events, so you can add unique flavor (and easily share back!) in a few linesWe have a ton of demos on the library site, along with all the knobs to play with how each aspect renders. Tool and reasoning, custom loading animations, voice, approval UX, etcWe've also added a ton of examples across agent and frontend stacksCheck out the code @ https://github.com/runtypelabs/personaFeedback and contributions welcome!
HN · launched Jun 20, 2026 · 27 upvotes (top 22%) · 0 views
Niche: ui component libraries · 312 launches, 18 in the last 7 days ▼ -38% · Explore this niche →
Category and tags
- Horizontal
- Dev tools
- Developer
- AI-native
- Hobby / open-source project
Visit website ↗ Source listing ↗
More like this: all 312 launches in ui component libraries →
Could you build this?
Yes It is an unopinionated vanilla JavaScript UI library implementing chat widgets and standard Model Context Protocol (MCP) browser clients.
Discussion
19 comments analyzed.
Competitors mentioned: assistant-ui, Claude Code for frontend design, Figma
Concerns raised: WebMCP adoption still very early and experimental, Spec may still evolve and break early adopter implementations, Not useful for designers building with Claude Code, WASM integration not yet widely accepted
Feature requests: Better DOM hooking and more efficient data formats over the wire, Improved shareability of created experiences in ecosystem, More extensibility hooks and custom extensions
Competitors
Other products that read as similar to this one : 238 launches clear the similarity bar, closest 8 shown.
Attention rank: #64 of 239 (itself plus its competitors, highest first, normalized so YC and Product Hunt are compared fairly).
Launched 228 days after the earliest competitor.
- Persona.js · ph · 2026-06-28 · 295 upvotes · similarity 0.70
- Persona · ph · 2026-11-13 · 1 upvotes · similarity 0.55
- PageAgent, A GUI agent that lives inside your web app · hn · 2026-03-05 · 147 upvotes · similarity 0.44
- Cursor for Userscripts · hn · 2026-01-28 · 56 upvotes · similarity 0.44
- Browser Tools SDK · hn · 2026-07-21 · 11 upvotes · similarity 0.43
- Rotunda · hn · 2026-05-13 · 13 upvotes · similarity 0.43
- Vibe-coded Steam, but in the browser · hn · 2026-05-23 · 8 upvotes · similarity 0.42
- Nectar, a Rust-like React that compiles to WebAssembly · hn · 2026-07-06 · 29 upvotes · similarity 0.42
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