Too / Either Adding short responses of agreement

Short Answers

TOO		NOT EITHER
We can use too to add a comment of agreement after someone makes a positive statement.		We can use either to add a comment of agreement after someone makes a negative statement.
POSITIVE I am excited.  (be verb)	Me too!  (informal) I am too! He is too! They are too!	NEGATIVE I am not worried.	Me either!  (informal) I am not either! He isn't either! They aren't either!
I have a backpack.   (have verb) backpack (n.) – book bag	Me too!  (informal) I do too!     (Br. Eng. have too) He does too!   (Br. Eng. has too) They do too!    (Br. Eng. have too)	I do not have a backpack.	Me either!  (informal) I don't either!     (Br. Eng. haven't either) He doesn't either! (Br. Eng. hasn't either) They don't either!  (Br. Eng. haven't either)
I would like a desk.   (modal verb)	Me too!  (informal) I would too! He would too! They would too!	I would not like to sit on the floor.	Me either!  (informal) I wouldn't either! He wouldn't either! They wouldn't either!
I hoped for a new school.   (past verb)	Me too.  I did too. He did too. They did too.	I did not like the old one.	Me either.  (informal) I didn't either. He didn't either. They didn't either.

Me too (informal speech) – is more commonly used in a present, immediate context, less commonly for an activity or action in the past.

Common Mistakes

ERROR	FIX
I'm not going, and he isn't going neither.	I'm not going, and he isn't either.     (Also see neither...or)
"I thought he was dead."  "Me too."	"I thought he was dead.."  "I did too."   We tend to use me too in a present, immediate context. (Me too is informal.)
I can't wait for the opening, and they can't too / also / as well.  (verb + not)	I can't wait for the opening, and they can't either. Use either after a verb with not: can't help, can't wait, can't stand, can't bear.
"I can hardly believe my eyes! "   (negative adverb) "Me too."	"I can hardly believe my eyes! " "Me either." (informal)  "I can't either. (neg. can+hardly = can+not) Use either after a negative adverb: hardly, barely, seldom, rarely, never.
"No one helped me."   (negative pronoun) "Me too."	"No one helped me." "Me either."  Use either after a negative pronoun: no one, nobody, not one person, none of them