Microsoft Editor analyzes your document and offer suggestions for spelling, grammar, and stylistic issues. You'll find it in the Word for Microsoft 365 and Word for the web. Plus there's an extension for Outlook and browsers.
To use Editor, on the Home tab choose Editor.
Select a suggestion to incorporate it into your document, or choose Ignore if you don't want to use the suggestion.
You might notice Editor’s red and blue underlines in your document even when the Editor pane is closed. That’s because Editor is always running in the background. Left-click the underlined text to see the suggestion.