The Best Free Market Data APIs for Algo Trading

You don't need a Bloomberg terminal to build algo trading strategies. Here are the best free/cheap data APIs I've used.

Stocks & ETFs

1. Alpha Vantage (FREE)

• What: Real-time and historical stock data
• Limit: 25 requests/day (free tier)
• Best for: Hobbyist backtesting, EOD strategies
• Gotcha: Rate limits hit fast. Cache aggressively.

2. Polygon.io ($29/month)

• What: Real-time + historical stocks, options, forex, crypto
• Why: Professional-grade data at indie pricing
• Best for: Serious backtesting and live trading
• Bonus: Webhooks for real-time price updates

3. Yahoo Finance (via yfinance)

• What: Free historical data via Python library
• Limit: None (unofficial scraping)
• Best for: Quick backtests, learning
• Gotcha: Unofficial—could break. Don't use for prod.

Crypto

4. CoinGecko API (FREE)

• What: Crypto prices, volume, market cap
• Limit: 10-50 calls/min (free tier)
• Best for: Multi-coin analysis, market scans

5. Binance API (FREE)

• What: Real-time crypto OHLCV, order book, trades
• Best for: High-frequency crypto strategies
• Bonus: Same API for trading if you use Binance

Alternative Data

6. FRED (Federal Reserve Economic Data) (FREE)

• What: Macro indicators (GDP, unemployment, rates)
• Best for: Macro-driven strategies
• Python: fredapi library

7. Reddit API (via PRAW) (FREE)

• What: Scrape r/wallstreetbets, r/stocks for sentiment
• Best for: Sentiment analysis, meme stock tracking
• Gotcha: Noisy data—requires heavy filtering

My Stack

For personal trading, I use:

• Polygon.io for real-time stock data ($29/mo)
• CoinGecko for crypto ($0)
• Yahoo Finance for quick backtests ($0)

Total: $29/month for professional-grade data. Way better than the $1k+ institutional options.

Pro Tips

1. Cache everything. Hit APIs once, store locally.
2. Use SQLite for local storage. Fast, simple, no DB server needed.
3. Respect rate limits. Add exponential backoff to API calls.

Drop your favorite data sources in the comments!