Prediction markets just hit $3.6B in volume. I wanted to know what the biggest traders were betting on — in real time. So I built WhaleTrack.
Here's how it works under the hood.
The Problem
Polymarket has a public leaderboard. But it only shows P&L totals — not what whales are currently betting on, not their recent activity, not their win rate. If you want to follow smart money, you're flying blind.
I wanted something that answered: what are the top traders doing right now?
The Stack
- Vanilla JS frontend (no framework, keeps it fast)
- Vercel serverless function as a backend proxy (avoids CORS issues)
- Polymarket's public data API — no auth required
Step 1: Finding the Whales
Polymarket exposes a leaderboard endpoint:
This returns their recent trades — market name, size in USDC, timestamp. Refreshes every 60 seconds.
Step 3: Calculating Win Rate (the tricky part)
The key is the redeemable flag — redeemable: true means they won, currentValue: 0 + redeemable: false means they lost. Took a few wrong attempts with cashPnl (always negative, not useful).
Step 4: The Whale Alert Banner
Every 60 seconds I check for trades over $5,000 placed in the last 10 minutes. When it fires, a green banner slides down with the whale name, market, and amount. Auto-dismisses after 12 seconds. First time I saw it fire live with a $28K bet — genuinely exciting.
Results
- 129+ users in the first few days
- Zero ad spend
- Traffic from Twitter, Reddit, Quora
What's Next
- More whale wallets (suggestions welcome)
- Click-through to open the same market on Polymarket directly
- Email/push alerts for big trades
Check it out: whaletrack.app
All feedback welcome — especially if you spot a whale I'm missing.
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