Wave buoys are the definitive way to know what is actually happening out to sea right now. Wave buoys close to the shore will give a good second check for the actual swell conditions before driving to the beach, and wave buoys some distance from the coast a reliable forward forecast of conditions over the next few hours (depending on distance).
Note that wave buoys can report slightly different metrics from the wave forecast data and can't always be directly compared. UK Wave Buoys
MSW imports live data from thousands of weather stations around the world every few minutes. Most stations are Airports or government facilities, this means that while they might not always be perfectly positioned for your local break they are carefully calibrated and report accurately. Some weather stations report hourly, some twice an hour. Some don't report overnight.