WebMCP is the browser-native agent-action protocol — Chrome shipped it in Canary Feb 2026 behind chrome://flags "WebMCP for testing." This audit probes any URL for the four declarative + capability signals a WebMCP-aware browser agent looks for. Preview-stage spec; first-mover positioning available now.
A JSON discovery file at /.well-known/webmcp declaring the site's WebMCP capabilities (similar to robots.txt or .well-known/ai-plugin.json patterns). Browser agents check this first to learn what actions the site supports.
An inline <script type="application/webmcp+json"> block declaring the page's specific actions. Lets agents understand what forms can be submitted, what API endpoints can be called, and what data fields are expected.
HTML attribute annotations like data-webmcp-action, data-webmcp-form, data-webmcp-input on existing forms. The Declarative API path lets static pages expose actions without writing JavaScript.
JavaScript that calls document.modelContext.registerTool({name, description, inputSchema, execute}) once per tool (navigator.modelContext is accepted as an alias). We string-match the page HTML and up to three WebMCP scripts it loads; true presence requires execution, which we don't do. The draft removed the older provideContext() call on 2026-03-05 (pull request 132), so a page that only calls provideContext(), or uses the never-standard window.webmcp names, gets a legacy warning and no points.
WebMCP is a W3C Community Group Draft (Feb 2026). Surface conventions may shift before stable release. This audit detects the most-cited declaration patterns from Chrome's WebMCP intro post. If your implementation uses different selectors, the score will under-report. Re-run after spec stabilization.