WebMCP Inspector

Inspect, debug, and augment WebMCP tools on any webpage — in real time.

WebMCP Inspector discovers both declarative (HTML form-based) and imperative (JavaScript API) tools exposed via the WebMCP specification. It lets you view schemas, edit attributes, execute tools, and test with Chrome's on-device Gemini Nano model, all through a live sandboxed browser session powered by Webfuse.

Live Demo

https://webmcpinspector.com

Features

Tool Discovery

• Declarative tools — Scans pages for HTML forms annotated with WebMCP attributes (toolname, tooldescription, toolparamtitle, toolparamdescription, toolautosubmit)
• Imperative tools — Detects tools registered via navigator.modelContext.registerTool() with full input schema support (requires Chrome 146+)
• Form augmentation — Turn any plain HTML form into a WebMCP tool by adding metadata through the UI. Overrides are saved per-URL in localStorage and restored automatically on revisit

Inspection & Debugging

• Schema viewer — View the generated JSON schema for any discovered tool
• Form highlighter — Locate and highlight forms directly on the target page
• Tool execution — Call any tool directly from the sidebar with typed parameter inputs and view results in real time
• Prompt Debugger — Chat interface powered by Chrome's built-in Gemini Nano model (via the Prompt API). The on-device agent autonomously discovers and calls tools based on natural language prompts
• Activity log — Real-time history of tool discovery, augmentation, execution, and navigation events

Environment

• Live preview — Target pages are rendered in a sandboxed Webfuse session alongside the inspector. No browser extension install required.
• Webfuse Extension — Included Manifest V3 content script for direct page introspection (used internally by Webfuse sessions)
• URL history — Recently visited URLs are saved and shown as autocomplete suggestions

Getting Started

Prerequisites

• Node.js 22+
• npm

Setup

git clone https://github.com/nichochar/webmcpinspector.git
cd webmcpinspector
npm install

Create a .env file from the example (required for dev mode):

cp .env.example .env

Fill in your Webfuse widget key and space ID for the development environment:

VITE_WIDGET_KEY_DEV=your_dev_widget_key
VITE_SPACE_ID_DEV=your_dev_space_id

Development

npm run dev

Opens at http://localhost:5173/inspect/.

Build

npm run build

Output goes to dist/.

Lint

npm run lint

Docker

docker build -t webmcp-inspector .
docker run -p 8080:80 webmcp-inspector

The app is served at http://localhost:8080/inspect/ with the landing page at /.

Project Structure

src/
  App.tsx              # Main app — session management, state, messaging
  components/
    Sidebar.tsx        # Tool/form listing, attribute editing, save/reset
    MainContent.tsx    # Iframe container (Webfuse session) + activity log
    PromptPanel.tsx    # Gemini Nano chat UI for tool execution via Prompt API
  types.ts             # Shared TypeScript interfaces
  analytics.ts         # Plausible analytics wrapper

public/
  extension/
    manifest.json      # Webfuse Extension manifest (Manifest V3)
    content.js         # Content script — form scanning, attribute patching,
                       #   imperative tool interception, message bridge
  landing.html         # Static landing page

How It Works

1. Connect — Enter a URL. Webfuse opens a sandboxed browser session rendering the target page
2. Scan — The content script scans the page for WebMCP-annotated forms and imperative tools registered via navigator.modelContext
3. Inspect — Discovered tools appear in the sidebar with their attributes, parameters, and generated schemas
4. Augment — Edit WebMCP attributes on any form or add them to plain forms. Changes are applied live via message passing and persisted in localStorage
5. Execute — Call imperative tools directly with parameter inputs, or use the Prompt Debugger to have Gemini Nano orchestrate tool calls from natural language
6. Debug — The activity log tracks all events. Schema viewer shows the exact JSON schema that would be exposed to an AI agent

Chrome Flags

Some features require experimental Chrome flags:

Feature	Flag	Chrome Version
Imperative tools (JS API)	chrome://flags/#enable-webmcp-testing	146+
Prompt Debugger (Gemini Nano)	chrome://flags/#prompt-api-for-gemini-nano	138+

Related Links

• WebMCP Specification
• Chrome WebMCP Announcement
• WebMCP Demo Pages
• Webfuse

License

MIT