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.
A window.webmcp JavaScript namespace with register() calls. We detect the namespace by string-matching the page's static JS — true presence requires execution which we don't do.
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.