Is it: He’s coming too or He’s coming, too
I don’t want one either or I don’t want one, either
The answer on this one is actually quite simple. You can please yourself.
There are no set rules, at least none that are applied regularly today. [Some people will try to make rules, but they don’t seem to work very well.] Just do what you think suits the situation.
Jim has a ball, so Mary wanted one too!
I think that works without the comma. But there’s nothing wrong if you put one in.
Jim worked in accounting at the time, but he had another job, too. He was a barman at night.
I like that better with a comma.
There is one case where the comma is used more often than not, and that is when the “too” is in the middle of the sentence.
Michael used to go sailing every Sunday, and his son went with him. His daughter, too, when she was old enough.
Inevitably, when I get a copyedit back from the publisher, I find she has inserted more commas than I originally put in. I usually leave them there. I figure that a copyeditor – while perhaps not the actual god of punctuation and grammar – does come close, and tends to know more than I do about what is best!
So don’t fuss too much about this one. No editor is going to toss your work across the room because you did or did not insert a comma before “too”.
That’s all I have time for this week – I have a copyedit that has to be completed and sent back to Australia …