D2L has added word count to the Discussions Tool. 

You must be in the Brightspace editor to see your word count. There are two ways you can see the word count while you are in a post or reply. One method shows the word count as you type your post or reply, and the count updates as you enter and or delete text.

Word Count displayed in lower left of editor.The other method uses the Brightspace Editor toolbar. Once you have typed your post or reply, you can click on the word count icon in the Brightspace Editor toolbar.

Word Count navbar icon.Next, a pop-up window will display a visual word count for the discussion post or reply. All words in a discussion post are counted and include filler words such as “the,” “if,” and “to.”

Pop-up Word Count.