What's the adjective for chatterest? Here's the word you're looking for.
Included below are past participle and present participle forms for the
verbs chat and chatter which may be used as adjectives within certain contexts.
chatty
(informal) Of a person, chatting a lot or fond of chatting.
(informal) Of a text or speech, expressed in a conversational style.
“Of course, the iPhone itself doesn't have any chat programs, like AIM, Yahoo Messenger, or MSN Messenger. But that doesn't mean you have to remain chatless.”