Persona.js

Persona, created and maintained by Runtype as an MIT-licensed open-source project, is a lightweight JavaScript library for building agent-powered user interfaces on the web, enabling developers to create conversational AI experiences that interact with page tools and functions through a standardized interface. Multiple layout options deploy as a floating widget, docked sidebar, or fullscreen assistant without changing agent logic, and WebMCP integration leverages the WebMCP standard to discover and safely execute page tools like search, carts, and forms with user approval built in. Style isolation uses Shadow DOM and prefixed CSS to prevent conflicts, flexible backend support works with any SSE backend including AI SDK, LangGraph, and OpenAI Agents, customizable theming offers a three-layer token system with dark mode, and the library is framework-agnostic, installing via npm or script tag.