No-IP Free hostnames must be no longer than 19 characters in length. They can contain the letters a-z, numbers 0-9, and the special character – (dash).

Plus Managed DNS, Enhanced DNS, and Pro Dynamic DNS hostnames can be up to 49 characters in length. They can contain the letters a-z, numbers 0-9, and the special character – (dash).

Basic Hostname Guidelines:

• You cannot have more than one dash within a hostname.
• A hostname cannot have any spaces, nor can it start with a dash.