WebMCP checker: see what AI agents can do on your site
Enter any page. Relvato loads it in a real browser, records every WebMCP tool it registers, reads its forms and validates the site's AI catalog — what Lighthouse's new Agentic browsing audits look at, without needing Chrome's WebMCP flag.
Free, no account. One page per check. Results are kept for 24 hours and shared for the same address; up to 5 checks every 10 minutes.
What an AI agent needs from your page
Registered tools
Every tool the page registers with document.modelContext.registerTool (or the older navigator.modelContext): its name, description and parameters, and whether it's marked read-only.
Form tools
Forms with toolname and tooldescription become tools an agent can fill in. Each field needs a name and a description or label — the same issues Chrome reports.
Form coverage
Forms that aren't tools yet, which Lighthouse lists in its WebMCP form coverage audit.
AI catalog
Found where Lighthouse looks (a robots.txt Agentmap line, a link tag, a Link header, /.well-known/ai-catalog.json) and validated against the same schema — one unknown field fails it.
llms.txt
Whether the site gives answer engines a curated map at /llms.txt.
Tool count
More than 40 tools on one page costs agents context and invites the wrong pick; Lighthouse warns above that.
Tools for the AI agent in the browser
WebMCP is a proposed web standard, developed in the W3C Web Machine Learning Community Group, that lets a page tell an AI agent in the browser which actions it offers. Instead of guessing from buttons and screenshots, the agent calls a named tool — search_products, book_table, contact_support — with parameters described in JSON Schema.
There are two ways to offer a tool. Imperative: your JavaScript registers it, with a function that runs when an agent calls it. Declarative: you add toolname and tooldescription to a form you already have, and the browser turns its fields into the tool's parameters.
Chrome ships WebMCP behind a flag and an origin trial (Chrome 149 and later), so most visitors don't have it yet. That makes now the time to add it: tools are cheap to register and do nothing where WebMCP isn't available.
Three snippets
A registered tool, a form tool, and the AI catalog that lists your agent-facing services.
if (document.modelContext) {
document.modelContext.registerTool({
name: "search_products",
description: "Search the store's products by keyword. Returns names, prices and links.",
inputSchema: {
type: "object",
properties: { query: { type: "string", description: "Words to search for" } },
required: ["query"],
},
annotations: { readOnlyHint: true },
async execute({ query }) {
const res = await fetch("/api/search?q=" + encodeURIComponent(query));
return JSON.stringify(await res.json());
},
});
}<form action="/newsletter" method="post"
toolname="subscribe_newsletter"
tooldescription="Subscribe an email address to the monthly newsletter.">
<label for="email">Email</label>
<input id="email" name="email" type="email" required
toolparamdescription="The address to subscribe">
<button>Subscribe</button>
</form>{
"specVersion": "1.0",
"host": { "displayName": "Example Shop" },
"entries": [{
"identifier": "urn:air:example.com:mcp:shop",
"displayName": "Example Shop MCP server",
"type": "application/mcp-server-card+json",
"url": "https://example.com/.well-known/mcp/server-card.json",
"representativeQueries": ["where is my order", "is this item in stock"]
}]
}What the Agentic browsing audits need
Lighthouse's Agentic browsing category, in PageSpeed Insights too, has three WebMCP audits — tools registered, schemas valid, form coverage — and an ai-catalog.json schema check. The WebMCP audits only run when the Chrome doing the audit has WebMCP switched on, which is why they often show as not applicable today.
The catalog check is live now: once a site has an ai-catalog.json, Lighthouse validates it strictly against the ARD schema, and an unknown top-level field is enough to fail it. This checker applies the same rules, so you can fix it before PageSpeed flags it.
Questions, answered
Do I need Chrome's WebMCP flag to use this checker?
No. The check runs in Relvato's own browser, which records the tools your page registers whether or not WebMCP is built in, and reads your forms directly.
Why does PageSpeed show the WebMCP audits as not applicable?
Lighthouse runs them only when the Chrome doing the audit has WebMCP turned on. Until Chrome enables it by default, PageSpeed will often skip them — this checker shows what they would find.
Is it safe to add WebMCP tools now?
Yes. Feature-detect (if (document.modelContext)) and nothing runs in browsers without WebMCP. Mark tools that only read with readOnlyHint, and leave toolautosubmit off on forms that send, buy or change something, so the person confirms.
What is ai-catalog.json?
A machine-readable list of the agent-facing services a site offers — an MCP server, an agent, skills — from the Agentic Resource Discovery (ARD) specification. Lighthouse reads /.well-known/ai-catalog.json; the newest spec version names /.well-known/ard.json, so serve the same file at both.
What happens to the pages I check?
Relvato loads the page once, in a browser that can only reach public addresses, and keeps the result for 24 hours so the same address isn't scanned again. Nothing else about the check is stored.
Can Relvato watch this on my site all the time?
Yes. The AI / AEO readiness check includes WebMCP and the AI catalog and runs again after every update or deploy, so a theme or plugin update that breaks your tools is flagged.
Know when an update breaks your agent tools.
Relvato's AI / AEO readiness check watches WebMCP, the AI catalog, llms.txt and AI crawler access on every change.