It is an educational blog post that explains what WebMCP is, how its discovery/schema/state model works, how a tool call flows between page and agent, and includes a minimal JavaScript code example for registering a tool via document.modelContext.registerTool.
It is most valuable now, while WebMCP is in draft/origin-trial stage, for developers prototyping AI-agent interactions, evaluating whether to expose site actions to agents, or wanting to shape and get ahead of a standard before it matures.