Polymarket Clone — Sports

A Polymarket-style prediction market for real sports games, played with fake money. Looks and feels like the real thing: cents-priced YES/NO shares, prices that move as volume comes in, live price charts, a portfolio with P&L — plus a built-in admin god-mode where you can force any result and watch the payouts land.

Not affiliated with Polymarket. For fun and learning only.

Features

• Real games, real teams — schedules, logos, colors, live scores and final results pulled from ESPN's free, no-key API (NFL, NBA, MLB, NHL, EPL, NCAA, UCL, La Liga…). Falls back to a bundled sample slate when offline so it always runs.
• Polymarket-style trading — outcomes priced in cents (0–100¢ = implied probability). Buy YES/NO shares through an LMSR market maker, so your trades actually move the price. Winning shares redeem for $1.00.
• Real sportsbook odds — show prices as American (-160 / +140), Decimal (1.63), or Percent, switchable from the settings menu. Opening prices are seeded from the real de-vigged moneyline in ESPN's feed.
• Onboarding — a polished first-run flow: welcome → follow your teams → you're set.
• Follow your teams — star any team; a Following tab surfaces just their games.
• Leaderboard — every bot keeps a real ledger (cash + positions, marked to market). Climb the ranks against 16 simulated traders; podium, medals, live P&L.
• Fake money — start with $10,000. An "Add funds" button tops up any amount.
• It feels alive — simulated bot traders nudge prices around fair value, generating volume and a wiggling price history. Live games drift toward whoever's winning.
• Animation & polish — confetti when you win, count-up balances, price-tick flashes, skeleton loaders, and smooth micro-interactions throughout.
• Live price charts + sparklines, portfolio P&L, and a global activity feed.
• Admin god-mode (/admin) — force-resolve any market (YES/NO) and instantly redeem your winning shares, set a price by hand, inject volume, toggle the bots, tune liquidity, pick leagues, add funds, and reset everything.
• Auto-resolution — when ESPN reports a game final, the market settles to the real winner and pays you out automatically.
• Everything persists to localStorage, so a refresh keeps your money and bets.

Run it

npm install
npm run dev
# open http://localhost:5173

Build for production:

npm run build && npm run preview

How it works

src/
  lib/
    espn.ts          # fetch + normalize ESPN scoreboards -> Market[]
    marketEngine.ts  # LMSR maths: price, cost, buy/sell, seeding from odds
    sampleData.ts    # offline fallback slate
    format.ts        # money / cents / time formatting
  store/
    useStore.ts      # zustand store: trading, resolution, bots, admin (persisted)
    selectors.ts     # derived P&L / portfolio read-models
    useSimulation.ts # bot heartbeat + ESPN polling
    useUI.ts         # toasts + modals
  components/        # NavBar, MarketCard, TradePanel, PriceChart, AdminMarketRow, …
  pages/             # Home, Market, Portfolio, Activity, Admin

The market maker (LMSR)

Each binary market is a Logarithmic Market Scoring Rule maker. The YES price is a softmax over outstanding YES/NO share quantities, always lands in (0, 1), and rises when YES is bought. Opening prices are seeded from the real sportsbook moneyline embedded in ESPN's feed (de-vigged), so day-one prices are honest. The liquidity parameter b controls depth — higher b means smaller price impact per trade.

Resolution

• Automatic: ESPN is polled every 30s; a game going final settles the market to the real winner and redeems your winning shares at $1.00.
• Manual (admin): force YES or NO from /admin and watch your balance jump.

Data source

ESPN's unofficial scoreboard API: https://site.api.espn.com/apis/site/v2/sports/{league}/scoreboard. Free, no key, CORS-enabled — so the whole app is a static SPA with no backend.

License

MIT