Select any text and tweet then right away. Twitter fast share also shows the number of word selected
Twitter fast share lets you share web pages to your Twitter feed with a click. You can select some text on any web page and hit the “Share on Twitter” button that appears besides the selected text.
As you are selecting text on a web page, this little tool will also display the exact character count of your tweet (see video) and thus you could save yourself from trimming characters later manually.