<, >, <=, >=) check if the value is less than, greater than, less than or equal, and greater than or equal to your search. atk>=4000 will show all cards with an ATK of at least 4000. These operators do not work for text fields.level:3|6|9 to find all cards that are level 3, 6, or 9.It is possible to filter for multiple values at once, e.g. level:3|6|9 to find all cards that are level 3, 6, or 9.
Searching by regex is supported. Simply put the search string in slashes, i.e. o:/draw \d+ card/. No regex flags can be passed, but i (case-insensitive) is enabled by default.