Chat Js

ChatJS is an open source foundation for building production AI chat applications, released under the Apache 2.0 licence. It gives developers a working chat product with authentication, streaming, tool calling and access to more than 120 models, so a team can start from a running application rather than wiring model routing and session handling from scratch. It is built for developers and product teams shipping an AI chat MVP or prototyping across several model providers. A single interface covers Claude, GPT, Gemini, Grok and Llama models, and users can switch providers in the middle of a conversation without losing context. Parallel responses send one message to several models for side by side comparison, and conversations can be branched to explore different directions. A Canvas feature creates and edits documents, code files and spreadsheets with version history and inline diffs. Built in tools include a multi step deep research agent, reasoning display, sandboxed Python and JavaScript execution, web search with inline citations, image generation and video generation. Authentication supports OAuth with Google, GitHub and Vercel, anonymous mode and rate limiting, and MCP support connects external tools. The stack is Next.js and TypeScript with the AI SDK, Better Auth, Drizzle ORM, PostgreSQL, Redis, Vercel Blob, shadcn/ui and Tailwind CSS. A hosted demo runs in the browser, and desktop builds are packaged for macOS, Windows and Linux. ChatJS itself is free to use under its open source licence, and no paid plans are published. Running it means paying for your own hosting, database and model provider usage. The desktop builds are currently unsigned, so the install guide explains how to get past the operating system warnings.