Evaluating me? Promising not to keep top secret? (9)
I believe the answer is:
measuring
'evaluating' is the definition.
('measure' can be a synonym of 'evaluate')
I cannot understand how the remainder of the clue works.
(Other definitions for measuring that I've seen before include "Quantifying" , "Determining the dimensions" , "Ascertaining size of" , "Ascertaining length, breadth, etc." .)