I look at the /MES S&P Futures to get an idea how the SPY and SPX might open. But I don’t necessarily trade the open. I’ve found that I lose the most money trying to capture opening volatility, and I get better results letting the market settle for 20-60 minutes. Trading breakouts is just one trading strategy of many. On my day off, I’ll look for breakouts off premarket highs and lows - doesn’t always happen - sometimes we get “chop” and those don’t work well for day trading. I’ll reference “tools” in your other question. 👍