WebMCP - Model Context Tool Inspector

May 19, 2026 ยท View on GitHub

A Chrome Extension that allows developers to inspect, monitor, and execute tools exposed via the experimental navigator.modelContextTesting Web API.

Prerequisites

Important: This extension relies on the experimental navigator.modelContextTesting Web API. You must enable the "WebMCP for testing" flag in chrome://flags to turn it on in Chrome 148.0.7778.56 or higher.

Installation

You can install this extension either directly from the Chrome Web Store or manually from the source code.

Install the extension directly via the Chrome Web Store.

Option 2: Install from source

  1. Download the Source: Clone this repository or download the source files into a directory.

  2. Install dependencies: In the directory, run npm install.

  3. Open Chrome Extensions: Navigate to chrome://extensions/ in your browser address bar.

  4. Enable Developer Mode: Toggle the Developer mode switch in the top right corner of the Extensions page.

  5. Load Unpacked: Click the Load unpacked button that appears in the top left. Select the directory containing manifest.json (the folder where you saved the files).

Usage

  1. Navigate to a Page: Open a web page that exposes Model Context tools.

  2. Open the Inspector: Click the extension's action icon (the puzzle piece or pinned icon) in the Chrome toolbar. This will open the Side Panel.

  3. Inspect Tools:

    • The extension will inject a content script to query the page.
    • A table will appear listing all available tools found on the page.

  4. Execute a Tool:

    • Tool: Select the desired tool from the dropdown menu.
    • Input Arguments: Enter the arguments for the tool in the text area.
      • Note: The input must be valid JSON (e.g., {"text": "hello world"}).
    • Click Execute Tool.

Disclaimer

This is not an officially supported Google product. This project is not eligible for the Google Open Source Software Vulnerability Rewards Program.