I use this site sometimes to find cards that are similar to one another. It’s automated so the comparisons don’t always fulfill the same role but it’s usefully different from lists that are curated by hand like https://www.mythicspoiler.com/. mtgassist.com has a similar feature but I prefer the results from Card Codex.
Compare the results from these two links
https://cardcodex.com/?card=Urborg%2C+Tomb+of+Yawgmoth#search
https://www.mtgassist.com/cards/From-the-Vault-Realms/Urborg-Tomb-of-Yawgmoth/
Seems it prioritizes rules text over casting cost. I put in Counterspell and the first page was 100% cards with mv3 or higher. Sometimes having the same mv is more important than having the same rules text, but I guess maybe that wasn’t the goal here.
That’s exactly correct. The similarity model basically ranks the importance of keywords based on how rare they are in the entire body of text. So for Counterspell “target” is pretty much irrelevant because so many things target but “counter” and “spell” are significant because they’re rarer. Then it more or less quantifies the similarity of any two cards by how frequently they use these important keywords.