Altcoin Season Index API
One number that tells you whether crypto capital is rotating into altcoins or huddling in Bitcoin, computed live from Binance daily candles (no key, nothing stored). The market swings between two regimes: in "altcoin season" most alts outperform Bitcoin and money chases the long tail; in "Bitcoin season" alts bleed against BTC and capital flees to the majors. The classic gauge is simple — of the top altcoins, what share has outperformed Bitcoin over the last 90 days? Above ~75% it is altcoin season; below ~25% it is Bitcoin season. The index endpoint returns that index (0-100), the season label, Bitcoin's own return over the window and how many alts out- versus under-performed. The leaderboard endpoint ranks the alts by their excess return versus Bitcoin — who is leading the rotation and who is lagging — each with its own return, BTC's return and the gap. The coins endpoint lists the universe. The altcoin-season / alt-vs-BTC rotation cut — distinct from the market-cap-dominance and global-market APIs (which report BTC's share of total cap, not relative performance), the single-coin momentum and the price APIs. It answers whether it is altseason, not what the market cap is.
api.oanor.com/altseason-api
