Before you sign up, all of the data is saved in your browser. Technically you could use it like this indefinitely, but this is mostly for demo purposes, so some of the functionality won't be available (like sharing data across devices, email reminders, public profile page). Also if I will make significant changes to my database in the future, this may cause issues. So that's not the best solution.

In the future I'm planning to create a desktop app, that might be the perfect solution if you really don't want your data to leave your computer.

Meanwhile, I can promise you that I will never share your data with anyone. I'm not using extra sophisticated encryption or anything like that (that would be an overkill for a writing app), but I'm using Atlas [1] to store your data (they're really good and competent database as a service provider), and on my end I've made sure that nobody can read what you wrote without your password.

There's no such thing as flawless security I suppose, but I'm trying to follow the best practices, so unless you're writing a short story about your social security number falling in love with your credit card pin code, or a novelization of NSA's deepest darkest secrets, I wouldn't worry too much about this =)

[1] https://www.mongodb.com/cloud/atlas