The Alpaca Trade Streaming API provides your Alpaca trading algorithm, with access to real-time price and fundamentals. It is the ability to place orders and manage your portfolio, with a streaming style that listens to one or more streams, and allows you to get updates on account and trade changes. WebSocket clients can listen to trade streams real-time data for any Alpaca accounts. This API can be authenticated using your Alpaca API key that must be sent with an authentication message over the WebSocket connection as its payload. Alpaca API provides a way to build and trade with real-time market data for free.