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sunpeak API

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Overview

Register tools that your app provides to the host. This enables bidirectional tool calling — the host can call tools defined by the app, in addition to the app calling server tools via useCallServerTool.

Wraps oncalltool · onlisttools

MCP Apps SDK reference

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Import

import { useAppTools } from 'sunpeak';

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Signature

function useAppTools(config: AppToolsConfig): void

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AppToolsConfig

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tools
AppTool[]
required
Array of tool definitions to register with the host.
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onCallTool
(params: { name: string; arguments?: Record<string, unknown> }) => CallToolResult | Promise<CallToolResult>
required
Handler called when the host invokes one of this app’s tools. Return a CallToolResult with the tool’s output.

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AppTool

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name
string
required
Unique tool name.
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description
string
Human-readable description of what the tool does.
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inputSchema
Record<string, unknown>
JSON Schema for the tool’s input parameters.

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Usage

import { useAppTools } from 'sunpeak';
import { useState } from 'react';

function EditorResource() {
  const [selection, setSelection] = useState('');

  useAppTools({
    tools: [
      {
        name: 'get-selection',
        description: 'Get the currently selected text',
      },
      {
        name: 'insert-text',
        description: 'Insert text at the cursor position',
        inputSchema: {
          type: 'object',
          properties: { text: { type: 'string' } },
          required: ['text'],
        },
      },
    ],
    onCallTool: async ({ name, arguments: args }) => {
      if (name === 'get-selection') {
        return {
          content: [{ type: 'text', text: selection }],
        };
      }
      if (name === 'insert-text') {
        // Insert text logic...
        return {
          content: [{ type: 'text', text: 'Inserted successfully' }],
        };
      }
      return { content: [], isError: true };
    },
  });

  return (
    <textarea
      value={selection}
      onChange={(e) => setSelection(e.target.value)}
    />
  );
}

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How It Works

  1. Your app registers tools via useAppTools when the component mounts.
  2. The host discovers tools via the MCP listtools protocol.
  3. When the host invokes a tool, your onCallTool handler is called with the tool name and arguments.
  4. Your handler returns a CallToolResult which the host uses in its next turn.

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See Also

useCallServerTool

Call MCP server tools from your app (the other direction).