Twitter is a social networking site that allows you to share information, announcements or daily musings with the world. When you sign up for a Twitter account, you must create a name that people will use to search for and identify the tweets you post. Twitter limits the characters you can use in your username. Although the "@" symbol appears with your Twitter name on your tweets, you do not include it with your username when you create it.
Twitter allows you to use all of the letters in the English alphabet. Twitter names do not have to contain a letter.
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You can use any of the numbers zero through nine for your Twitter name. The username does not have to contain a number.
Since spaces are not allowed in a Twitter name, you can use an underscore to separate words, letter and numbers. An underscore can start and end the name, and you can place multiple underscores together.
Twitter does not differentiate between upper- and lowercase letters in a username when people search for that name or when you sign in to your account. However, you can use upper- and lowercase letters in your name, and it will appear that way on screen.
The maximum length for a Twitter name is 15 characters. This includes all letters, numbers and underscores.