Free WebMCP validator

Check if your website is AI agent–ready. Validates declarative HTML tools, the navigator.modelContext JavaScript API, and the /.well-known/mcp.json discovery endpoint. No registration required.

Works with any publicly accessible URL — no login needed.

What is WebMCP?

WebMCP (Web Model Context Protocol) is an emerging W3C standard — developed jointly by Google and Microsoft — that lets websites expose structured tools so in-browser AI agents can take actions directly, without needing to visually parse the UI or click through forms. Chrome 146+ supports it behind the chrome://flags/#webmcp-for-testing flag.

What this validator checks

Declarative HTML Tools

Detects form[toolname] elements and validates tool names, descriptions, and input parameter quality against the W3C spec.

Imperative JS API

Checks for navigator.modelContext.registerTool() and related API calls in page scripts.

MCP Discovery Endpoint

Probes /.well-known/mcp.json and /.well-known/mcp/server-card.json for SEP-1649 / SEP-1960 compliance.

HTTPS Requirement

navigator.modelContext requires a secure context. HTTP pages cannot use the WebMCP browser API.

Agent-Readiness Score

Aggregates all signals into a 0–100 score (grade A–F) so you can track progress as you implement WebMCP.

Tool Quality Audit

Flags missing descriptions, invalid tool names, undocumented parameters, and dangerous autosubmit settings.

Two ways to implement WebMCP

1 — Declarative HTML (no JavaScript)

Annotate existing forms with WebMCP attributes. The browser auto-generates JSON Schema from the form fields.

<form toolname="search_products"
      tooldescription="Search catalog by keyword">
  <input type="text" name="query" required
         toolparamdescription="Search terms">
  <button type="submit">Search</button>
</form>

Add toolautosubmit for read-only actions (search, filters). Omit it for write actions to require human review.

2 — Imperative JavaScript API

if ("modelContext" in navigator) {
  navigator.modelContext.registerTool({
    name: "add_to_cart",
    description: "Add a product to cart",
    inputSchema: {
      type: "object",
      properties: {
        product_id: { type: "string" }
      },
      required: ["product_id"]
    },
    execute: async ({ product_id }) => {
      await cart.add(product_id);
      return { content: [{ type: "text",
        text: "Added to cart" }] };
    }
  });
}

MCP well-known discovery endpoint

Place a JSON file at /.well-known/mcp.json so AI clients can auto-discover your MCP server before connecting. Two formats are in use:

SEP-1960 Endpoints Manifest

{
  "mcp_version": "2025-11-25",
  "endpoints": [{
    "url": "https://example.com/mcp",
    "transport": "streamable-http",
    "capabilities": ["tools","resources"]
  }]
}

SEP-1649 Server Card

{
  "protocolVersion": "2025-11-25",
  "serverInfo": {
    "name": "My MCP Server",
    "version": "1.0.0"
  },
  "transport": {
    "type": "streamable-http",
    "url": "https://example.com/mcp"
  },
  "capabilities": {
    "tools": true, "resources": false
  }
}

Browser support: WebMCP is available in Chrome 146+ Canary behind the chrome://flags/#webmcp-for-testing flag (as of April 2026). The W3C specification is maintained by the Web Machine Learning Working Group.