The $250 Surprise That Changed My Data Pipeline
I was pulling daily OHLCV data for 500 tickers using yfinance when Alpha Vantage started rate-limiting me. The free tier caps at 25 API calls per day — I hit that limit by 9am.
Switching providers isn't just about finding free alternatives. It's about understanding the hidden costs: rate limits that block your backtest at 3pm, websocket fees that only appear after you scale past 100 symbols, and "free" tiers that suddenly require $50/month when you add one more ticker.
Here's what actually matters when comparing stock data APIs: cost per million calls, survivorship bias in historical data, and whether the "free" tier will still work when your strategy monitors 200 symbols instead of 20.
yfinance: Free Until Yahoo Decides It Isn't
yfinance scrapes Yahoo Finance HTML. No official API, no guaranteed uptime, no support when it breaks.
The appeal is obvious: zero cost, zero signup, unlimited tickers. I've used it for every backtest that didn't need sub-minute data. But "free" comes with three catches.
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