While the user types his new password, or after keyboard focus leaves the text field, show
an estimate of the password strength beside the text field. At minimum, display a text and/
or graphic label indicating a weak, medium, or strong password, and special wording to
describe a too-short or invalid password. Colors help: red for unacceptable, green or blue
for good, and some other color (often yellow) in between.
If you can, show additional text with specific advice on how to make a weak password
better—a minimum length of eight characters (for instance), or the inclusion of numbers
or capital letters. A user might get frustrated if he repeatedly fails to produce a valid password,
so help him be successful.