This API is the only intraday historical API available to the public that has very high intraday resolution since the year 2004 for 660 stocks. This should a provide a unique API for algorithmic trading developers to back-test their strategies. This API provides stock market data in 30 minutes and one hour interval. Also, SPX data is available in 1 hour, 30 minutes, 5 minutes and 1 minute resolution.