forms - Error message for "Invalid Username"

As per "UX guidelines" what should be the error message for a dimmpley Login for having 2 basic fields "Username" & Password.

So if a User Enter a username with "Space or special characters[,/<>{}]", should the message be very general saying "Invalid Username" or "Please enter a valid username"? or should it be more specific by telling them the special charaters they have added are not acceptable for this filed?

Here is what I am doing right now!

Please suggest!

Answer

If your page clearly states what character are and are not valid when registering, then a generic message such as "Invalid Username" is just fine.

If not, then it would definitely be helpful to show the username guidelines when you give the error. Another option that you have is when the user is actually typing in a username, you could have a tooltip that pops up with the username guidelines (gmail does this). This way you could maintain a minimal design and keep the page aesthetically pleasing, while also giving important and relevant information.

I don't think it's ever necessary to specifically SHOW which characters that the user has used are invalid. That's a lot of extra code for something that doesn't add much value to the experience.

Attached are ways Amazon and GMail handle username error checking