It's definitely early - it shipped in the very latest version of chrome just this week, and the spec may still evolve (as a fair warning to early adopters).

You can turn it on for your site via the chrome origin trial, or just install the polyfill.

Our use case with Persona is all about extending existing apps to have "AI assistance" that actually works well, and Persona being the AI assistant you can ship yourself in your site to enhance your app. There's a parallel camp who are interested in adding WebMCP tools to their sites so they can be used effectively by future browser-level agents (e.g. Gemini in Chrome), but that's not a thing today.

Some AI agents can already do best-effort operation of existing websites via naive 'headless browser' approaches, or doing their best to interpret the existing nature of a page by reading the DOM or accessibility tree and trying to submit the forms, but that's flaky and token-inefficient. WebMCP is all about registering those things as explicit, designed tools built for agents. I'd draw a parallel between asking agents to just call existing REST APIs for an app vs intentionally designing MCP APIs for them; the design philosophy is different.

For those interested in good MCP/WebMCP tool design principles, this article from Arcade.dev is great: https://www.arcade.dev/blog/mcp-tool-patterns/