I build TrickyBird, a web proxy, so I'm not neutral here. This is a build note about the part that came before the tool: what we had to switch off first. WebMCP lets a page give the browser's agent a real function instead of a DOM to guess at. You call document.modelContext.registerTool({ name, description, inputSchema, execute }) , and the agent can list the tool and call it. The feature sits behind a Permissions Policy whose default is self . On a normal site that default does the isolati...