What is WebMCP?
WebMCP is a W3C Community Group draft proposal (backed by Google and Microsoft) that lets AI agents interact with websites through the browser. Instead of scraping or using separate APIs, sites annotate their existing HTML forms with attributes that declare them as callable tools.
How it differs from MCP
| | MCP (Anthropic) | WebMCP |
|---|---|---|
| Agent talks to | Your server directly | The browser, which talks to your server |
| Auth | OAuth 2.1 / API keys | Browser's existing cookies and session |
| Transport | JSON-RPC over HTTP/SSE | Browser internal API (navigator.modelContext) |
| What you build | A dedicated endpoint | Annotations on existing HTML forms |
| Lifetime | Persistent connection | Ends when user closes the tab |
Despite the name, WebMCP does not use MCP's JSON-RPC protocol. It borrows the "tools" concept but is a separate spec.
Current status
WebMCP is a Draft Community Group Report (April 2026). It is available behind an experimental flag in Chrome Canary but is not shipped in any production browser. The spec may change.
What AgentGrade checks
WebMCP manifest — We check for /.well-known/webmcp.json, a discovery file that lists tools your site exposes.
Form tool annotations — We check your homepage HTML for elements with tool-name attributes.
Both checks are optional and informational — your score is not penalized for missing them.
How to implement
1. Annotate forms:
<form tool-name="search" tool-description="Search products by keyword">
<input type="text" name="query" tool-param-description="Search query">
<button type="submit">Search</button>
</form>
2. Publish a manifest at /.well-known/webmcp.json:
{
"spec": "webmcp/0.1",
"tools": [
{
"name": "search",
"description": "Search products",
"url": "/search",
"method": "GET",
"parameters": [
{ "name": "q", "type": "string", "description": "Search query" }
]
}
]
}