If you’ve ever struggled to strike the right tone in an email, the FoxType Politeness Checker might be just the thing for you. The free web app analyzes your word choices, and tells you whether you come across as polite or rude. Which is great if you’re struggling to write a particularly sensitive email—or if you’re just interested in the way language works.

Just paste your text in the box, and click “Check Tone.” The app automatically rates your word choices on a scale from one to 100. A 50/100, for instance, denotes a “neutral” email, while 0/100 means you’re being unutterably rude. 

But the app doesn’t just rate your word choices—it also offers suggestions and feedback, breaking down your sentence into “impolite” and “polite” components. Negative words like “no,” “can’t,” and “won’t”? No good. “Dear,” “good,” and “best wishes”? Great. 

It’s a great tool for anyone interested in learning how their word choices might be interpreted by others. But beware of simply copying and pasting the app’s re-writes into your emails: some of their suggestions may be polite, but they’re not always grammatical. Check it out here

[h/t: Lifehacker]