Are you looking at sheet music and trying to figure out the chord names? If so, I agree with Simon that an App is unnecessary. This sheet of chords will tell you more than you need. I don't think you need more than C, CMaj6, CMaj7, CMin6, CMin7, C7, Cdim (Co) , Cdim7 (Co7) , CAug (C+). If you have crazy chords, at your stage of development you're better off just saying "that's almost a C7, with some extra stuff" and continuing your analysis from there. (Just remember that the 5th of a chord is often omitted in jazz.)
I sometimes write out chords names on sheet music (both jazz and classical) because it helps me when I can't be bothered to read out all the notes in a chord. But that only works because I've practiced reading from lead sheets. Is this a skill you're trying to obtain? If so I'd recommend trying to sight read lead sheets. When you're proficient, then writing the chords can really help you get through a piece with less worry about missing a note and feeling you can't continue because you've jumped the rail.
If you're writing chords only to help you with interpretation (assuming you have the theory knowledge to understand how the chords can help with interpretation), then go for it! I still don't think you would need an app for that.
But, If you are trying to learn a piece by listening to a recording, then an app could be useful (though if you're doing that, you're probably at a level where figuring out chords by ear is a very useful practice).
