For the last two years I have been studying various methods of checking username availability across many popular social media services. In my research, I have found many people struggle to understand how YouTube determines whether a slug is available to claim as a custom url. My goal of this article is to explain to the best of my ability how it all works.

To truly understand how custom urls work, you must understand that YouTube has three different url formats—a base url, a user url, and a channel url. The base url is the normal youtube.com url with the only thing after the trailing slash is either the owner of the channel's username or, if the user already has a custom url, the channel's custom url slug. The user url follows this format youtube.com/user/{username}, where {username} is the username of the channel owner. The channel url is reserved only for channels that meet the criteria for a custom url and have already claimed one. It looks like this, youtube.com/c/{channel slug}, where {channel slug} is the custom url slug that the owner chooses.

When checking to see if a custom slug is available, a request is made to each of the url formats and upon receiving the HTTP status code of each of the requests, you can accurately determine the availability of a particular YouTube custom url. An HTTP status code of 404 means the slug is available in that particular format. However, for the custom url to be available, a 404 must be returned for all three url formats with no exceptions.

There is one gotcha to look out for as this process is not foolproof. YouTube, like all other social media services, has some restricted words on a private blacklist. Under no circumstances can these words be registered as a custom url by anyone. It is safe to assume that the list would contain some fairly obvious words like "admin" or the numerous trademarks held by YouTube and Google, but don't rule anything out. A specific name could be blacklisted for a number of reasons and it usually is just trial and error figuring out which ones are on the list. If the custom url that you want is on the list, you are out of luck and should find another name.

To sum up, YouTube custom urls have specific rules regarding what is considered available to claim and what is not. It is not hard to determine once you understand the logic behind how it all works. Just remember that there is a blacklist of certain terms that will never be available to register unfortunately.

Cross-posted to LinkedIn Pulse