CopilotKit: Open-Source React Building Blocks for Agent UIs

CopilotKit is an MIT-licensed open-source library (30k GitHub stars) that provides React building blocks for the agent UI layer. It handles the pain points of building real agent apps: streaming, tool call rendering, state sync, and generative UI. Instead of being locked into a specific stack like Vercel's AI SDK, CopilotKit is framework-agnostic on the backend.

Key Features

• UI components: chat interface, streaming output, tool call rendering, human-in-the-loop (HITL), and generative UI.
• AG-UI protocol: an open standard that the UI layer speaks, with pre-built adapters for LangGraph, ADK, Strands, CrewAI, Mastra, Pydantic AI, LlamaIndex, Agno, and others.
• Bring your own everything: agent, model, backend, hosting — no per-framework adapter needed.
• Horizontal integration: same UI works across any supported agent framework.

Why It Matters

Existing agent frameworks still make it difficult to build real applications. Even a basic in-app chatbot requires handling streaming, tool calls, and state synchronization. Vercel's AI SDK simplifies starting but ties you to Vercel's stack and is opinionated about the agent framework. CopilotKit separates the UI layer from the agent logic, letting developers use their preferred tools.

Getting Started

Repository: github.com/CopilotKit/CopilotKit

The project has strong community involvement, particularly around the AG-UI open protocol. Users report a great experience building with it.