What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Username and password are both not allowed.
While technically "username" is something that would not allow you to enter into some account, it might be used for social hacking and similar, but what it will do, is that it will cause you issues with your form/account.
Basically you should be OK using it, but at any point, your form can be removed, or your form and account suspended, depending on the circumstances around the form.
Taking all that into account, I would personally suggest to not use it on your forms.