WebMCP and browser agents: when an AI agent visits your website

A proposed web standard from engineers at Google and Microsoft that lets a website offer tools an AI agent in the browser can call, like starting a quote, so it doesn't have to read and click its way through the page. It was first published in August 2025 and is being developed in a W3C community group.

Chrome and Edge both have it in origin trials that sites can sign up to, though Chrome's own Gemini agent doesn't call the tools yet. The browser in ChatGPT's desktop app already calls WebMCP tools. Safari and Firefox don't support it yet (Apple has said it opposes it, and Mozilla is neutral), so the details may still change.

Fill them in the way a person would, from what they can read on the page. The main ones are designed to pause for the customer before submitting a form, signing in or paying, but neither the agent nor your form knows which answers were guesses.

It's early, but ChatGPT's browser already uses it, and every agent that calls your tools is one that isn't guessing its way through your form. Because the journey behind the tools lives in Marrow, a change to the standard means updating the tools, and the sale behind them stays as your compliance team signed it off.

We run it on onmarrow.com today, and the tools there start the same journey Marrow runs in ChatGPT and Claude. If you'd like to see it, or talk about putting it on your own site, get in touch.

We'd say yes, on your own terms. It's worth deciding which pages and actions they can reach, sending the ones that say who they are to tools like these, and keeping out the ones collecting prices with no customer behind them. That's work for your web and security teams rather than part of Marrow's product, but it's something we help clients plan.

Not specifically. The FCA-commissioned Mills Review in July 2026 called for the foundations of agentic finance, including mandates and auditability, and warned that an agent applying for a product arrives at a firm with no verified identity.