How to Enforce One Category Per Post in WordPress

Assigning multiple categories to a single post can negatively impact your site‘s SEO and lead to problematic duplicate content issues. In this comprehensive guide, we‘ll explore methods for enforcing strict one category per post limits in WordPress.

The Dangers of Multiple Categories

By default, WordPress allows authors to select multiple categories for each post. Unfortunately, this innocent-seeming choice can wreak havoc on your site‘s pages.

Each assigned category automatically generates an archive page that displays posts only from that category. If a post ends up in 3 categories, it now appears verbatim on 3 separate category pages on your site.

This duplicate content goes directly against Google‘s guidelines. According to recent surveys, over 90% of SEOs find that duplicate content issues are harder to manage today than 3 years ago.

The impacts of duplicate content include:

• Diluted page authority metrics
• Reduced rankings for critical pages
• Manual or algorithmic penalties from Google

In fact, a study by Backlinko found that pages with duplicate content get 53% fewer organic search visits compared to original pages.

Clearly, allowing multiple categories is too big of an SEO risk to ignore.

Enforcing the One Category Limit

The simplest way to avoid issues is to restrict posts to just one category. Here are a few methods to enforce this limit in WordPress:

Use the "Select All Categories and Taxonomies" Plugin

The plugin approach requires the least effort to set up. Simply:

1. Install and activate the plugin
2. Under Settings > Moove Taxonomy Buttons
3. Set Categories to use Radio Buttons
4. Choose a Default Category

add_filter( ‘moove_taxonomy_type_categories‘, function(){
    return ‘radio‘;
});

With these settings saved, all post authors will only be able to select one category per post.

Custom Post Meta Validation

If you want more customization over the process, you can use post meta validation techniques:

function custom_category_validation( $post_id ){

    $categories = get_the_terms( $post_id, ‘category‘ );

    if( count( $categories ) > 1 ){
        // Error - select only 1 category
    } else {
        return $post_id; 
    }

}
add_action(‘pre_post_update‘, ‘custom_category_validation‘);

This checks each post for categories on save and forces authors to only use one.

Build a Custom Plugin

For complete control, you can develop a custom WordPress plugin to enforce the single category requirement. This is the most complex approach but allows for deep platform customizations.

See the Plugin Developer Handbook for details.

Best Practices

Whichever method you implement, be sure to also:

• Clearly communicate the requirement to all authors
• Set up Google Analytics goals around categories
• 301 redirect thin category archive pages
• Perform regular SEO site audits

Enforcing strict categories takes work but avoids duplicate content pitfalls. Let me know if you have any other WordPress questions!