Coinflip

Inspiration

Sports betting has grown rapidly across the United States since legalization, including here in Kansas. While billions of dollars are wagered each year, nearly all of that activity happens through sportsbooks that build a house edge directly into their odds. Even when two friends disagree about a game and want to challenge each other, there isn’t really a structured way to do that fairly — both sides usually end up betting into the same sportsbook market and paying that built-in margin. Coinflip started from a simple question: what if sports wagers worked more like peer-to-peer markets instead of sportsbooks? Instead of betting against the house, users challenge their friends directly inside private groups. By removing sportsbook margin and normalizing odds to fair probabilities, Coinflip creates what we call a true 50/50 sports market where the outcome is determined only by the game itself.

What it does

Coinflip is a friends-only peer sports market that allows users to challenge each other directly on game outcomes without a sportsbook acting as the counterparty. Users create identities, add trusted friends, and form private groups that function as small markets where offers can be posted and accepted. Each offer is tied to a real NBA game and structured as a head-to-head wager between two participants. The system removes the traditional sportsbook margin and converts odds into fair probabilities, meaning neither side is paying a hidden fee to the house. Once a wager is settled, Coinflip records verifiable artifacts of the outcome using blockchain transaction hashes and IPFS receipts, creating a transparent settlement trail.

How we built it

Coinflip was built as a full-stack web application using modern web technologies. The frontend interface is built with Next.js, React, TypeScript, and Tailwind CSS, creating a simple dashboard where users can create identities, add friends, join private groups, and post head-to-head offers on live NBA games. Behind the interface, Next.js API routes act as the backend layer that handles users, friendships, groups, and wager offers. Sports data is retrieved through The Odds API, which provides live game information and sportsbook markets. Those markets are processed to remove the built-in margin so that Coinflip can present fair odds between two participants instead of traditional sportsbook pricing.

Built With

• espn-scoreboard-api
• json
• next.js
• node.js
• pinata/ipfs
• react
• tailwind-css
• the-odds-api
• typescript
• xrpl-(ripple)