* Adverb: This is the most common function of "too." It modifies a verb, adjective, or another adverb, indicating an excess of something. For example:
* "The soup is too salty." (modifies the adjective "salty")
* "He ran too fast." (modifies the adverb "fast")
* "They slept too long." (modifies the verb "slept")
* Determiner: "Too" can be used as a determiner to mean "also" or "in addition." For example:
* "I want to go to the party too."
* Preposition: In very rare cases, "too" can act as a preposition meaning "in addition to" or "as well as." For example:
* "I want to go to the party too Jane." (This usage is less common and often considered informal)
Therefore, the most common word class for "too" is an adverb, but it can also function as a determiner or, less frequently, as a preposition.