Windows only (for now): ToneCheck is an email plug-in that checks the content of your emails for tone and alerts you to language that may be misunderstood or interpreted as particularly negative.
Let's face it: Sometimes you send an email that you fully intend to convey anger or annoyance. But text communication is rife with misunderstandings, and often an email with perfectly pleasant intentions can lead to a lot of upset coworkers. That's what ToneCheck aims to address.
After installing the plug-in (available for Outlook only for now, but it looks like versions for Gmail, Thunderbird, and Mail.app are in the works), you'll get a new Run ToneCheck button right next to Spellcheck in Outlook. Click it to see an analysis of the tone of your email (like the one in the screenshot above). From that point, you can edit out the offending language, or you may want to adjust your settings to change the tolerance threshold for both negative and positive language.
During its beta, ToneCheck is a free download that works for a year, and is currently available for Outlook only. In theory it's a clever idea, but after testing it out a bit, I'm not sure it's ready to provide any serious impact in the way we communicate. In fact, I found a lot of its results downright frustrating, and it's mission, illustrated below as transforming emotional human beings into mildly contented automatons, is downright terrifying.
This may just be one of those arenas where you're better off practising a little good old-fashioned common sense.