Proof of competence? Officials won't have tons (8)

I believe the answer is:

diplomas

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

But I can't explain it at all! Could you help me understand?

(Other definitions for diplomas that I've seen before include "Qualifications" , "Certificates of examinations passed" , "Written records of achievements" , "Certificates of passing examinations" .)

I've seen this clue in The Times.

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