Using categories and tags as meta keywords

Your categories and keywords are valuable bits of metadata, but WordPress doesn’t use them in its meta tags. Even the popular All in One SEO Pack plugin uses only categories, not tags.

To use both, add this to the head section of your theme:

  foreach((get_the_tags()) as $tag) {
    $keywords[] = strtolower($tag->name);
  }
  foreach((get_the_category()) as $category) {
    $keywords[] = strtolower($category->cat_name);
  }
?>
" />

The last line removes duplicates and joins the keywords with a comma — just the way search engines like them.