> ## Documentation Index
> Fetch the complete documentation index at: https://sunpeak.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# useRegisterTool

> Register app-side tools the host can call.

<Badge color="yellow">sunpeak API</Badge>

## Overview

Returns a function to register tools that the host (or LLM) can call. Uses Standard Schema (Zod, ArkType, Valibot) for input/output validation. The returned handle supports `enable()`, `disable()`, `remove()`, and `update()`.

For simpler static tool registration, see [`useAppTools`](/app-framework/hooks/use-app-tools). `useRegisterTool` provides lower-level control with dynamic registration and Standard Schema support.

## Import

```tsx theme={null}
import { useRegisterTool } from 'sunpeak';
```

## Signature

```tsx theme={null}
function useRegisterTool(): (
  name: string,
  config: RegisterToolConfig,
  cb: AppToolCallback
) => RegisteredAppTool | undefined
```

### RegisterToolConfig

<ResponseField name="title" type="string">
  Human-readable title for the tool.
</ResponseField>

<ResponseField name="description" type="string">
  Description of what the tool does.
</ResponseField>

<ResponseField name="inputSchema" type="StandardSchemaV1">
  Input validation schema (Zod, ArkType, Valibot, etc.).
</ResponseField>

<ResponseField name="outputSchema" type="StandardSchemaV1">
  Output validation schema.
</ResponseField>

<ResponseField name="annotations" type="ToolAnnotations">
  Tool annotations (readOnly, destructive, idempotent hints).
</ResponseField>

## Returns

<ResponseField name="registerTool" type="(name, config, cb) => RegisteredAppTool | undefined">
  Function to register a tool. Returns `undefined` if app is not connected.
</ResponseField>

### RegisteredAppTool

<ResponseField name="enable()" type="() => void">
  Enable the tool.
</ResponseField>

<ResponseField name="disable()" type="() => void">
  Disable the tool.
</ResponseField>

<ResponseField name="remove()" type="() => void">
  Remove the tool registration.
</ResponseField>

<ResponseField name="update()" type="(updates) => void">
  Update the tool configuration.
</ResponseField>

## Usage

```tsx theme={null}
import { useRegisterTool, useSendToolListChanged } from 'sunpeak';
import { useEffect } from 'react';

function SelectionTool({ selectedText }: { selectedText: string }) {
  const registerTool = useRegisterTool();
  const sendToolListChanged = useSendToolListChanged();

  useEffect(() => {
    const handle = registerTool(
      "get_selection",
      { description: "Get the user's current text selection" },
      () => ({
        content: [{ type: "text", text: selectedText }],
      })
    );
    if (handle) {
      sendToolListChanged();
      return () => {
        handle.remove();
        sendToolListChanged();
      };
    }
  }, [registerTool, sendToolListChanged, selectedText]);

  return <div>Selection tool registered</div>;
}
```