You determine a crystal structure of a known protein which does not previously have a known structure, and compare the prediction to the experimentally determined structure.

There is a biennial (biannual?) competition known as CASP where some new structures, not yet published, are used for testing predictions from a wide range of protein structure prediction (so, basically blind predictions which are then compared when the competition wraps up). AlphaFold beat all the competitors by a very wide margin (much larger than the regular rate of improvement in the competition), and within a couple years, the leading academic groups adopted the same techniques and caught up.

It was one of the most important and satisfying moments in structure prediction in the past two+ decades. The community was a bit skeptical but as it's been repeatedly tested, validated, and reproduced, people are generally of the opinion that DeepMind "solved" protein structure prediction (with some notable exceptions), and did so without having the solve the full "protein folding problem" (which is actually great news while also being somewhat depressing).

By data I meant between the client and server, nothing actually related to how the program itself works, but just the fact that it's controlled by a proprietary third party.