The macOS has a very sophisticated spellcheck system which works quite well in all of the Apple Apps. Many third party Apps like Ulysses, which I am using to write this article, tap into the macOS spellcheck system. I am sure most people just take spellcheck for granted, but there are many things you can do to tweak it to your workflow. This very thorough article explains how to setup and use spellcheck on your Mac. If you do any writing at all, you owe it to yourself to read the article.