How to lowercase Yoast WordPress SEO Meta Keywords

If you need to make lowercase the WordPress SEO by Yoast meta keywords output, you can simply filter the output.

Make sure that under “Sitewide meta settings” you have checked “Use meta keywords tag?”.

Then, if you’d like you can use the “Meta keywords template” and adding something like this:

%%title%% %%page%%

This will display your meta keywords tags with initial caps (capitalization of the first word).

Use the following filter to lowercase all words output by the Yoast WordPress SEO plugin for your meta keywords:

/*
 * strtolower WordPress SEO meta keywords
 */
function strtolower_wpseo_metakeywords( $content ) {
    return strtolower( $content );
}
add_filter('wpseo_metakeywords', 'strtolower_wpseo_metakeywords');

That’s it. If you’re using the WordPress SEO by Yoast meta keywords template and prefer those keywords output in lowercase, then filtering the content as seen above will do that for you.