Wysiwyg grammar checking from the proofreadbot.com online service! You have one free check per week, or you can buy a package for as low as 1 cent per check.
How to use it?
1. Select any text on webpage (Press left mouse button at start of text, drag until the end of text, release the left button, alternatively you can also press Ctrl + A inside a text box when you are typing.)
2. Right mouse button click on highlighted text
3. In the menu click on "Check with Proofread Bot..."
4. You will be taken to proofreadbot.com where the selected text is pasted into a text field and checked for issues.
At the moment English is supported, but more languages are planned. You can also contribute grammar checks, so read the contributor's guide, and you can start creating checks for your own language, and possibly make some money as well.
Types of checks