TwIDder ver 2.0 updated at 10/17/2014
The twitter ID-UserName converter - Convert from twitter user name into twitter ID, or vice versa.
The difference between UserName and ID number in twitter
Twitter user name (so-called twitter ID) and twitter ID number is either "unique key". In other words, each key is not duplicate with others. You can specify a user if you refer to one of the keys.
The ID number is,"primary key" in addition to "unique key". Primary key is used to identify him primarily. Therefore, you can not change the primary key. Normally twitter user are not aware of ID number.
On the other hand, The user name is not primary key. So you can change your user name to other unique one. Because twitter determine a user by his ID number, you can change your user name at any time.
How can you make use of ID - UserName converter?
Because twitter keeps following list using user ID numbers internally, your following people will not disappear from your time line even if they change their user name.
But if you do not follow the person and read his tweet on web site (that is, if you read it on " http://twitter.com/#!/somebody " ), you'll miss him easily.
If you know the user ID number of the person beforehand, you'll find his new user name using the converter of this page.