“You don’t sound too happy.” Is the word "too" an:

1. Noun
   
2. Pronoun
   
3. Adjective
   
4. Verb
   
5. Adverb
   
6. Preposition
   
7. Conjunction
   
8. Interjection
   

I feel like it should be 5 (adverb)? Thankyou!