I'm great at composing jazz (7)

I believe the answer is:

ragtime

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

'jazz' is the definition.
(type of jazz)

'i'm great at composing' is the wordplay.
'i'm great' anagrams to 'RAGTIME'.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for ragtime that I've seen before include "Scott Joplin's genre" , "Style of piano music" , "Kind of music" , "Syncopated piano music - migrate (anag)" , "Scott Joplin genre" .)

I've seen this clue in The Globe and Mail.

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