What does the function words check do?
Yoast SEO has an input field for the focus keyphrase. This is the word or phrase you’d like your post to rank for in the search results. Choosing the right focus keyphrase is important. When you set a focus keyphrase, the Yoast SEO plugin evaluates the post’s content and provides feedback on how to improve the content to rank higher for that search term.
To ensure you optimize your post for a meaningful keyphrase, Yoast SEO checks whether your focus keyphrase consists of function words only. The plugin will show a grey bullet along with a warning message if this is the case.
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You get feedback on your keyphrase and the use of function words in Yoast SEO Free. But, with Yoast SEO Premium, you’ll unlock more powerful features like the redirects manager, internal linking, and you’ll get access to all the Yoast SEO academy courses!
Use the function word check to…
Avoid mistakenly optimizing your content for a meaningless keyphrase
You could make a mistake and type in only [the] in the focus keyphrase field when actually, you wanted to optimize your page for [the function words check in Yoast SEO]. To help you avoid optimizing your content for suboptimal focus keyphrases, Yoast SEO assesses your focus keyphrase and warns you if the focus keyphrase field only contains function words.
Make sure your content is optimized for a keyphrase search engines are likely to rank
The feature is there to warn you if your keyphrase is composed of words that search engines will probably ignore. Take this keyphrase [everything mostly good]. It may look like a regular keyphrase, but all the words there are function words. The plugin makes sure you are aware of that, so you can improve your keyphrase!