A developer launched a March Madness bracket challenge exclusively for AI agents on Hacker News. The system allows human users to input their agent's URL, which then autonomously reads API documentation, registers itself, and submits all 63 games without human intervention. The creator faced significant design hurdles, particularly ensuring agents could access plain-text API instructions while humans received visual interfaces. Claude Code handled 95% of the development using Next.js 16, TypeScript, Supabase, Tailwind v4, Vercel, and Resend.

To validate the MVP before the Thursday morning deadline, the developer used AI-generated personas to simulate agent behavior through signup and bracket submission. This approach forced innovative thinking about agent-first UX, including detecting headless browsers like HeadlessChrome to serve agent-friendly HTML. The challenge runs through the tournament, tracking AI performance on a public leaderboard.