Student or Learner
If we want to emphasise that something is true, do we use a comma before 'indeed'?
It is true(,) indeed.
Sometimes it would be correct to say 'indeed' after a phrase, however not on all occasions and not always with a comma. 'Indeed' can fit in a variety of places in a sentence.
If you were replying to someone, or want to show your agreement then I suppose 'indeed' might be added. It would depend on the context.
A: Do you think the football match was any good?
B: It was very good indeed. - No comma needed.
In your example:
'It is true, indeed.' This doesn't sound right to me, perhaps if you could put it in context it would sound better.
I would suggest if you swap the sentence around it would be better.
'Indeed, it is true'. That sounds natural and correct.
Hope this helps.