Webmcp Extension

WebMCP Scout

DevTools for the agentic web.

WebMCP Scout is a Chrome extension that detects, visualizes, and tests WebMCP tools registered on any web page — and audits HTML forms for agent-readiness via the WebMCP Declarative API.

Built during Chrome's WebMCP Early Preview Program (Chrome 146+).

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What is WebMCP?

WebMCP is a proposed web standard that lets websites expose structured tools to in-browser AI agents — replacing fragile screen-scraping with robust, schema-driven tool invocation. Think of it as MCP, but native to the browser.

• Imperative API: Register tools via navigator.modelContext.registerTool()
• Declarative API: Annotate HTML ` elements with toolname and tooldescription` attributes

WebMCP Scout gives you visibility into both.

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Features

• Tool Detection — Detects imperative and declarative WebMCP tools registered on the active tab in real time
• Schema Visualization — Displays full JSON Schema definitions for every registered tool
• Manual Execution — Execute tools directly with custom input arguments, bypassing the LLM layer for deterministic testing
• Form Scanner — Audits HTML forms for WebMCP Declarative API compatibility, surfacing agent-readiness gaps and annotation opportunities
• Overlap Filtering — Filters forms already covered by imperative tools to eliminate false positives
• Sensitive Field Detection — Identifies password, payment, and PII fields with inline safety warnings
• Live Badge — Real-time badge showing tool count (green) and scannable form count (red)

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Requirements

• Chrome 146.0.7672.0 or higher
• WebMCP flag enabled

Enable the WebMCP flag

1. Open Chrome and navigate to chrome://flags/#enable-webmcp-testing
2. Set the flag to Enabled
3. Relaunch Chrome

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Installation

WebMCP Scout is not yet on the Chrome Web Store. To install manually:

1. Clone or download this repo
2. Open Chrome and navigate to chrome://extensions
3. Enable Developer mode (top right toggle)
4. Click Load unpacked
5. Select the repo folder

The Scout icon will appear in your toolbar. Navigate to any page with WebMCP tools registered and click the icon to open the side panel.

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Usage

Tools Tab

Shows all WebMCP tools detected on the current page — name, description, and full input schema. Click any tool to expand and execute it manually with custom JSON arguments.

Scan Tab

Audits all `` elements on the page for WebMCP Declarative API compatibility. For each form, Scout shows:

• Suggested toolname and tooldescription values
• Inferred JSON Schema for form fields
• Sensitive field warnings
• Missing annotation flags

Forms already covered by registered imperative tools are filtered out automatically.

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Background

WebMCP Scout was built as a hands-on exploration of the WebMCP Early Preview Program. As AI agents move from screen-scraping to structured tool invocation, developers need observability tooling to build and debug agent-ready web experiences.

This extension is part of broader work at the intersection of agentic SEO, AI agent infrastructure, and emerging web standards.

Learn more at amrin.dev

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WebMCP Resources

• WebMCP Early Preview Docs
• WebMCP GitHub Spec
• Chrome Labs Demos
• Chrome AI Dev Preview Discussion Group

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Status

Early preview / active development. Built against the March 2026 WebMCP spec.

Notable spec changes tracked:

• toolparamtitle removed (Mar 12, 2026)
• provideContext / clearContext removed (Mar 6, 2026)

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License

MIT — see [LICENSE](./LICENSE)

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Contributing

Issues and PRs welcome. If you find a page where Scout misbehaves or misses tools, please open an issue with the URL and a description of what you expected.

Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: amrinbuilds
• Source: amrinbuilds/webmcp-extension
• License: MIT

Install and usage instructions live in the source repository linked above.