If a non-developer calls it a "<something> number" it's definitely a string for me. Even if you need to occasionally perform arithmetic on these "numbers", you

If a non-developer calls it a "<something> number" it's definitely a string for me. Even if you need to occasionally perform arithmetic on these "numbers", you could still store them as strings and parse on-demand. In my experience, performing a culture-specific decimal.TryParse() at form submission time is the most robust way to validate something like a wire transfer amount. You can also do regex replace javascript stuff, but there are always some dragons in that realm (especially as you cross borders). Your backend is almost always going to be a better place to parse and verify user input.