It shows the first two characters, the last one, and the length. A value is
masked whole whenever fewer than five characters would stay hidden, so nothing
under eight characters long gives any of itself away:
monkeys preview SHORT_ONE
SHORT_ONE ... 6
A length and a two-character prefix are enough to tell a key pasted whole from
one that lost a character on the way, or one provider's key from another's. To
read a value in full, open Keychain Access or your keyring's own browser, where
the decision to look at a secret is yours and deliberate.
monkeys help ends with the same ground written for an agent to read: spend a
value through run, pass on the message when one is missing, and leave storing
to a human.