Hourly swell, secondary swell, wind sea, wind and tide come from global wave and weather models. Each swell component is converted to the size reaching the beach from the beach orientation and the swell direction and period, then combined by wave energy. Wave power is 0.49 × height² × period (kW per metre of crest). A rating from 1 to 5 compares size, power, wind, tide and swell direction with what the spot and the surfer's level (beginner, intermediate, advanced) prefer.
Copernicus Sentinel-2 passes a spot every 2 to 5 days at about 11:30 UTC. We crop a 2.2 km square around the spot, discard cloudy passes, and measure whitewater: bright pixels that are dark in short-wave infrared. From the foam we find peaks (A-frames, lefts and rights), how far the foam reaches from the shore, and, over the last weeks, the sandbanks that keep producing waves. A 2-D Fourier transform of open water gives the spacing and direction of swell lines.
Pixels are 10 m, so small waves are not visible. A picture shows one moment, clouds hide about a quarter of the passes, and rocks, islets and harbours can look like foam. We treat the satellite as evidence of where banks usually form, not as a live measurement, and we compare it with models and buoys.
Every guide lists its sources and a confidence level (high, medium, low). A "verified" badge means the position and direction were checked by hand.