The Altcoin Season Index measures the percentage of a cached liquid-altcoin sample that has a higher N-day ROI than the season standard (default: Bitcoin). When fewer than 25% of altcoins outperform BTC, it's Bitcoin Season — BTC is outperforming most altcoins. When more than 75% of altcoins outperform BTC, it's Altcoin Season — altcoins are broadly rallying. The shaded green zone (0–25) marks Bitcoin Season territory, and the red zone (75–100) marks Altcoin Season. Data source: server-cached CryptoCompare daily OHLCV. This public version currently uses ETH, BNB, and SOL so the page loads reliably without dozens of client-side API calls. A full top-50 static dataset should be generated server-side before expanding this index again.