Open any deck of yours on CHOOMDEX and the PREDICT tab (Choom+) gives you its expected win rate in ranked play, from what players who run your three Legends win among human players, nudged for the cards in your list.
Below it: your deck against every color combination, human results beside the simulator's; the cards that move your number up or down; your deck against today's top lists; and head to head against any of your decks or any shared deck. A switch sets the seat, going first or second, and every simulator figure follows it.
The simulator figures come from our own engine, which played a million games among thousands of decks so a model could learn which decks beat which. It is honest about its limits: the human number is the one to plan a tournament around, and the Codex explains how both are built. Sleeve the deck that wins, not the one that looks best on paper.