Persona.js – a vanilla-JS agent UI library with native WebMCP (MIT)
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 support So, why'd we do this? 1) We're super fans of the web and the browser can do a ton today 2) 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 with If you've been a part of huge apps with multiple frameworks inside them, or work inside CMS /…
In plain words
Persona.js is a vanilla JavaScript library for building AI agent interfaces in web browsers without requiring a framework dependency. It includes native WebMCP support and is designed for developers working in environments where adding a new framework is impractical, such as CMS platforms, website builders, or applications with multiple existing frameworks. The library is open source under the MIT license.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
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 support So, why'd we do this? 1) We're super fans of the web and the browser can do a ton today 2) 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 with If 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 months If 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 nice Everything has hooks and events, so you can add unique flavor (and easily share back!) in a few lines We 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, etc We've also added a ton of examples across agent and frontend stacks Check out the code @ https://github.com/runtypelabs/persona Feedback and contributions welcome!
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