How to Pick a Low-Latency US Stock API: Key Metrics & WebSocket Test

As a FinTech tech lead, I’ve onboarded several real-time market data feeds for US equities. The performance gap between a well-optimized API and a generic one can be over 200ms — enough to turn a profitable strategy into a loser. Here’s how I evaluate them, complete with code. Breaking Down Latency Latency comes from three main places: Transport: HTTP adds overhead; WebSocket delivers push in real time. Location: Servers near exchange data centers send data faster. Serialization: JSON parsing sl