The WebMCP Challenge is live — OpenAI with Chrome, Cloudflare, Shopify, Vercel, Render, and Netlify, running Aug 25–Sep 3 on Devpost, with $35k in prizes. Ten days to build something with WebMCP: the browser API that lets a page hand AI agents real tools to call instead of making them click through your UI.
I maintain an open-source WebMCP tool (disclosed bias — link at the end), so I've watched a lot of these builds. The projects that demo cleanly and the ones that fall apart in front of an agent differ on exactly two things. If you're building this week, here they are.
1. Expose actions, not a chat box
The reflex is to register a chat or ask tool that wraps a search box. Don't. An agent already is the chat interface — it doesn't need another one. What it can't do is your site's actions: search your catalog, add to cart, check availability, book a slot, submit the form. Register those.
document.modelContext.registerTool({
