Joky judge left us squirming (7)

I believe the answer is:

jestful

I'm a little stuck... Click here to teach me more about this clue!

'joky' is the definition.
I can't tell whether this defines the answer.

'judge left us squirming' is the wordplay.
'judge' becomes 'J' (abbreviation for judge).
'squirming' is an anagram indicator (I've seen this in other clues).
'left'+'us'='leftus'
'leftus' anagrammed gives 'estful'.
'j'+'estful'='JESTFUL'

Can you help me to learn more?

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app