Prefix WordPress Custom Post Type Names

When you call the register_post_type() function to register a custom post type, the first parameter is a unique string to identify the post_type you’re creating. Since this string needs to be unique, it is a bad idea to use a string that others might use (e.g. book).

If another plugin does try to register the same “unique” custom post type, things break. It is bad when things break so please use a prefix on your post type. Below I’ll walk you through the URL problems that occur when you use a prefixed post type and how to fix them.

Register a WordPress Custom Post Type

Here we are registering a custom post type, without prefixing the post type string. This is a bad idea.

While the URLs look good, we are using a post type of book which has a high probability of collision (i.e. another plugin using the same post type).

Do NOT use this code

function fe_register_cpt_fe_book() {
    $args = array(
      'public' => true,
      'label'  => 'Books',
      'has_archive' => true,
    );
    register_post_type( 'book', $args );
}
add_action( 'init', 'fe_register_cpt_fe_book' );

Now when I create an example post called “Anathem”, I have the following:

• http://example.com/book/anathem/ (Single Post Page)
• http://example.com/book/ (Archive Page of CPT book)
• http://example.com/wp-admin/edit.php?post_type=book (wp-admin page listing book posts)

Register a Prefixed WordPress CPT

Here we are going to use a prefixed post type name, which is good. Unfortunately, this has a negative impact on our URLs.

Do NOT use this code either

function fe_register_cpt_fe_book() {
    $args = array(
      'public' => true,
      'label'  => 'Books',
      'has_archive' => true,
    );
    register_post_type( 'fe_book', $args );
}
add_action( 'init', 'fe_register_cpt_fe_book' );

You’ll notice the only thing I’ve changed is the first parameter for register_post_type(), I’ve changed book to fe_book.

This results in the following URLs.

Note: If you’re trying this at home, you’ll have to recreate the Anathem post because WordPress will no longer find it (since the previous post was type book rather than fe_book).

• http://example.com/fe_book/anathem/ (Single Post Page) Problem
• http://example.com/fe_book/ (Archive Page of CPT fe_book) Problem
• http://example.com/wp-admin/edit.php?post_type=fe_book (wp-admin page listing fe_book posts)

You’ll notice I’ve marked two URLs as problems. We don’t want our public facing URLs to have fe_book. We would rather have books in the URL.

Register a Prefixed WordPress CPT with Rewrite

Here we use a prefixed post type and use the rewrite parameter to get the URLs we want.

This is the solution we want

function fe_register_cpt_fe_book() {
    $args = array(
        'public' => true,
        'label'  => 'Books',
        'has_archive' => true,
        'rewrite'     => array(
            'slug' => 'books',
        ),
    );
    register_post_type( 'fe_book', $args );
}
add_action( 'init', 'fe_register_cpt_fe_book' );

You’ll notice this time we added rewrite with a slug of books to the $args array.

This results in the following URLs.

• http://example.com/books/anathem/ (Single Post Page)
• http://example.com/books/ (Archive Page of CPT fe_book)
• http://example.com/wp-admin/edit.php?post_type=fe_book (wp-admin page listing fe_book posts)

Bonus Points for Plugin Authors Filtering the Slug

If you are going to be distributing your code, I strongly recommend you add a filter to the slug. This allows a developer to programmatically override your URLs, without modifying your code.

'slug' => 'books',

becomes

'slug' => apply_filters( 'fe_rad_book_plugin_slug', 'books' ),

where fe_rad_book_plugin_slug is a name that uniquely identifies your plugin (and ends in slug). If two custom post types both try to use the same slug, they won’t work properly. However, with this filter, we can easily change the slug and correct the collision.

Sal Ferrarello (@salcode)

Sal is a PHP developer with a focus on the WordPress platform. He is a conference speaker with a background including Piano Player, Radio DJ, Magician/Juggler, Beach Photographer, and High School Math Teacher. Sal can be found professionally at WebDevStudios, where he works as a senior backend engineer.