CopilotKit is an open-source SDK (software development kit, a set of libraries) for adding AI agents and chat to the user interface of an application, made by the company CopilotKit. It started as a React library and now also supports Angular, Vue, React Native, Slack and Microsoft Teams.
A developer adds a ready-made chat component, restyles it with the app's own components, or uses headless APIs (logic without a built-in look) for full control. The agent can render real UI components, such as a chart or a form, inside the conversation (generative UI); share a synchronized state that both the agent and the front end read and write; call tools; and pause to ask the user for confirmation before an action (human-in-the-loop). It connects to agent frameworks such as LangChain, Mastra and the Claude Agent SDK through AG-UI, an open protocol for the link between an app and an agent backend, which the company created.
The SDK is free under the MIT License. CopilotKit Intelligence, which adds persistent threads, user memory and analytics, is a paid platform billed per completed agent request.