Wordcounter shows a real-time word count as you type in any Google Docs document. You can toggle it off and on by clicking on the icon in the top right corner of your browser.
It also adds milestone markers every 500 words. Motivating!
Measure is a Chrome extension measuring typographic line lengths right from the page.
Generally speaking, a good measure is between 45–80 characters per line. This little tool helps you find it with a simple click in the toolbar and highlight of a line of text.