The IBM Watson Tone Analyzer add-on is now available in developer preview on the Twilio Add-ons Marketplace. This service uses linguistic analysis to detect and interpret emotions, social tendencies, and language style cues in textual communication. It can be used for various purposes such as flagging angry messages, enhancing chatbots, and analyzing text marketing campaigns. The API returns a visualization of response fields that provide insights into customer tone, allowing developers to identify how their customers are feeling.