MCP Apps ontoolinput - Complete Tool Arguments

MCP Apps SDK

import { App } from "@modelcontextprotocol/ext-apps";

Overview

The ontoolinput notification handler is called when the host sends complete tool arguments. This event arrives after a tool call begins and before the tool result is available, giving your app a window to process or display the finalized input. Like all notification handlers, ontoolinput should be registered before calling connect() to ensure no events are missed during the initialization handshake.

Signature

app.ontoolinput = (params) => void;

Parameters

params.arguments

Record<string, unknown>

Complete tool call arguments as key-value pairs.

Usage

Basic usage

const app = new App({ name: "MyApp", version: "1.0.0" });

app.ontoolinput = (params) => {
  console.log("Tool arguments:", params.arguments);
};

await app.connect();

Rendering tool input in the UI

app.ontoolinput = (params) => {
  const { code, language } = params.arguments as {
    code: string;
    language: string;
  };

  const editor = document.querySelector<HTMLPreElement>("#editor")!;
  editor.textContent = code;
  editor.dataset.language = language;

  highlightCode(editor);
};

Using with the sunpeak framework

The sunpeak framework provides the useToolData hook, which wraps ontoolinput (along with related handlers) into a reactive value for React components. This is the recommended approach when building with sunpeak.

import { useToolData } from "sunpeak";

function MyComponent() {
  const toolData = useToolData();
  // toolData.input contains the complete tool arguments
}

Event Handlers overview — all notification and request handlers
ontoolinputpartial — stream partial arguments as they arrive
ontoolresult — handle the tool execution result

​Overview

​Signature

​Parameters

​Usage

​Basic usage

​Rendering tool input in the UI

​Using with the sunpeak framework

​Related

Overview

Signature

Parameters

Usage

Basic usage

Rendering tool input in the UI

Using with the sunpeak framework

Related