It might seem odd to start a treatise on level shifting this way, but the first question for the designer when looking at making a 3.3V part talk to a 5V part should be this: Do I even need a ...

While we’re well into the age of 3.3V logic ... if the ESP8266 is 5V tolerant after all. If it is, great. We don’t need level converters, and interfacing the ESP to USB TTL serial adapters ...