Original Post — Direct link
Code Definition Sample / Description
m: or mana: Mana Cost m:x (all "X" spells), m:gg (cards with two green mana symbols in the casting cost)
a: or art: Artist a:poole (cards with Mark Poole as Artist)
f: or flavor: Flavor Text f:forehead
loy: or loyalty: Loyalty loy>=6 (planeswalkers that enter the battlefield with six or more loyalty)
?basicland Basicland only usefull with type land selected
?commander Commander can be a Brawl commander
?companion Companion can be a companion
?booster Boostable is found within boosters
-?booster Non Boostable is not found within boosters
?transform Transform Cards can transform
?split Split Cards has two split sides
?adventure Adventure Cards Creatures with Adventures
?spell Spells Everything but lands
?permanent Permanents Everything but instants and sorceries
?styled Styled Cards has purchasable a card style

All operators can be negated with a - in front of it.

If you want to hide the Expert Search Terms popup, move your mouse out of the search field after clicking in it to type.

I use the booster search term to check what rares am I missing from a set.
?booster r:R q<4 e:M21 for all missing rares from m21.

Also some useful additions from u/StrikingHearing8 that aren't explained in the overlay as well:

You can use parantheses and OR and AND, e.g. t:dog OR t:cat

You can search for mana symbols in the text by o:"{ow}", o:"{ou}", o:"{ob}", o:"{or}" and o:"{og}", as well as o:"{oc}" for the colorless symbol (the little diamond symbol) and o:"{o1}", o:"{o2}", ..., o:"{oX}" etc. for 1, 2,..., x colorless.

You can search for the tap symbol by o:"{ot}"

External link →
about 4 years ago - /u/WotC_BenFinkel - Direct link

Originally posted by StrikingHearing8

I'm not sure if it really has a meaning. It's just what they use as code for the symbols in oracle text, so I memorize it as o for oracle.

I like to imagine it represents the circle around the mana/cost symbol. #wotc_staff

about 4 years ago - /u/wotc_kale - Direct link

Originally posted by CockroachED

Getting some unexpected results with these. Does anyone have insight in the ?booster or -?booster results for Jumpstart, looks like there are actually booster packs for half the cards.

?booster works by checking the collector number vs collector number max. In a normal set, this is the same as the two number is the bottom left corner of the card (CN/Max)

[[Alpine Watchdog]] for example is 002/274, so it can be found in a booster.

[[Kaervek, the Spiteful]] is 358/274 so it cannot be found in a booster.

For Jumpstart the collector numbers might be a little funky, because the set is a bunch of reprints and doesn't have a normal booster formation. I think the Collector Max is 78, representing the new cards. The reprints may have carried over some of their collector information from the set they were released in, especially the ones we replaced.