If you wouldn't want someone to yell the name at you across a room to get your attention, it might be too complicated for a username.
Choosing a great name for your Tumblr blog is all about matching your vibe—whether that’s aesthetic, minimalist, or fandom-focused. Your name is actually two things: your (the link to your blog) and your Blog Title (the display name at the top). Quick Rules for a Perfect Name Nombres para Tumblr
Usernames must be between 3 and 20 characters and can include letters, numbers, and underscores, but no spaces . If you wouldn't want someone to yell the