Comma Before Too

When using the word too, you only need to use a comma before it for emphasis.

I, too, like bananas.

You can tell by the position of too that emphasis is required in this sentence, so we use the commas to offset it.

Mike wanted to go to the party, too, so he shut down his computer.

I like bananas, too.

This sentence doesn’t need a comma.

Read this book, and this one too.