Which Hook for Which Job

CopilotKit v2 has a focused set of hooks for letting the agent do things in your app and for rendering what it does. They split into two groups: hooks that register behavior, and hooks that register how a tool call looks in the chat. Use this page as the quick map, then follow each hook to its full reference.

The 30-second version

Hook	Use it when you want to
useFrontendTool	Give the agent a client-side tool to call (run logic in the browser), with optional inline UI.
useRenderTool	Render the UI for a specific tool call by name (typed), without defining the tool's handler.
useDefaultRenderTool	Provide one wildcard renderer for any tool call that has no specific renderer.
useComponent	Register a React component as a named tool renderer (component-first generative UI).
useHumanInTheLoop	Pause the agent on a tool call and wait for the user to approve, edit, or supply input.
useInterrupt	Handle an agent-initiated interrupt and resume execution once the user responds.
useRenderToolCall	Get a render function for tool calls to drive your own custom chat surface (headless).

How to choose

Start with the verb.

• "The agent should run something in my app." Use useFrontendTool. You define the tool's schema and handler; the agent calls it. Add a render to also show inline UI for the call.
• "The agent's tool call should look like something." Use a render hook. Use useRenderTool to render one named tool, useComponent to bind a React component to a tool name, or useDefaultRenderTool as the catch-all for anything you didn't render explicitly.
• "The agent should stop and ask me before continuing." Use useHumanInTheLoop for tool-level approval/edit gates, or useInterrupt for agent-driven interrupts you resume with user input.
• "I'm building my own chat UI." Use useRenderToolCall. It returns the renderer function so you can place tool-call output anywhere in a headless layout.

Tool vs. renderer

Two hooks in this set register a tool the agent can call: useFrontendTool (schema and handler) and useComponent (a component-first shorthand that wraps useFrontendTool internally, registering a tool whose "handler" is rendering your component). The render-only hooks, useRenderTool, useDefaultRenderTool, and useRenderToolCall, don't define a tool; they only render tool calls, which can come from your frontend (useFrontendTool / useComponent) or from the agent/backend. That's why you can pair a backend tool with useRenderTool and never write a handler on the client.

Related

• Frontend Tools: the full guide to useFrontendTool.
• Generative UI: rendering tool calls as rich UI.
• Human in the Loop: approval and interrupt patterns.
• Hooks reference: every v2 hook in detail.