Many people remember a rule from high school grammar class: When we use "too" to mean "also," it should be surrounded by commas in the middle of a sentence or preceded by a comma if it's at the end. Over at the Chicago Manual of Style, someone remembered an editor who put even more flourish on this rule: using the commas with "too" when it applies to an item in a list, but not when it refers to the subject of the sentence.

Too complex for me! And too much weight for one comma to bear.

Remember, "too" is an adverb. Use commas with "too" when it makes sense to use commas with any other short adverb. If you use "too" at the beginning of the sentence and you are placing commas after introductory adverbs, use one after "too." If you would use a comma before a final adverb, use it before "too."

Most of the time, you won't. Some of the time you will. I change my mind, too. But I stay consistent within the context of a book, article, letter, or email, as well.