---
tags:
  - wordpress
  - fse
  - php
  - taxonomies
  - categories
  - tags
title: Registering Custom Taxonomies for FSE
---

# Registering Custom Taxonomies for FSE

Just as Custom Post Types (CPTs) organize your content, Custom Taxonomies group that content. Whether you need "Project Types" (like Categories) or "Skills" (like Tags), registering them manually in `functions.php` ensures your theme is self-contained.

For Full Site Editing (FSE), the most critical argument is `show_in_rest`, which enables the taxonomy in the Block Editor.

## 1. Hierarchical vs. Non-Hierarchical

There are two main types of taxonomies:

*   **Hierarchical (Like Categories):** Can have parents and children. Uses checkboxes in the editor. Best for strict grouping (e.g., "Department", "Service Type").
*   **Non-Hierarchical (Like Tags):** Flat structure. Uses an input field with comma separation. Best for ad-hoc descriptors (e.g., "Skills", "Tools Used").

## 2. The Registration Code

Add this function to `functions.php`. You can register multiple taxonomies in one function or separate them.

```php
function my_register_project_taxonomies() {
    
    // 1. Hierarchical Taxonomy: "Project Types"
    $labels_type = array(
        'name'              => _x( 'Project Types', 'taxonomy general name', 'textdomain' ),
        'singular_name'     => _x( 'Project Type', 'taxonomy singular name', 'textdomain' ),
        'search_items'      => __( 'Search Project Types', 'textdomain' ),
        'all_items'         => __( 'All Project Types', 'textdomain' ),
        'parent_item'       => __( 'Parent Project Type', 'textdomain' ),
        'parent_item_colon' => __( 'Parent Project Type:', 'textdomain' ),
        'edit_item'         => __( 'Edit Project Type', 'textdomain' ),
        'update_item'       => __( 'Update Project Type', 'textdomain' ),
        'add_new_item'      => __( 'Add New Project Type', 'textdomain' ),
        'new_item_name'     => __( 'New Project Type Name', 'textdomain' ),
        'menu_name'         => __( 'Project Types', 'textdomain' ),
    );

    $args_type = array(
        'hierarchical'      => true, // TRUE = Category style (Checkboxes)
        'labels'            => $labels_type,
        'show_ui'           => true,
        'show_admin_column' => true,
        'query_var'         => true,
        'rewrite'           => array( 'slug' => 'project-type' ),
        'show_in_rest'      => true, // REQUIRED for Block Editor
    );

    // Register and attach to 'portfolio' CPT
    register_taxonomy( 'project_type', array( 'portfolio' ), $args_type );

    // 2. Non-Hierarchical Taxonomy: "Skills"
    $labels_skill = array(
        'name'                       => _x( 'Skills', 'taxonomy general name', 'textdomain' ),
        'singular_name'              => _x( 'Skill', 'taxonomy singular name', 'textdomain' ),
        'search_items'               => __( 'Search Skills', 'textdomain' ),
        'popular_items'              => __( 'Popular Skills', 'textdomain' ),
        'all_items'                  => __( 'All Skills', 'textdomain' ),
        'edit_item'                  => __( 'Edit Skill', 'textdomain' ),
        'update_item'                => __( 'Update Skill', 'textdomain' ),
        'add_new_item'               => __( 'Add New Skill', 'textdomain' ),
        'new_item_name'              => __( 'New Skill Name', 'textdomain' ),
        'separate_items_with_commas' => __( 'Separate skills with commas', 'textdomain' ),
        'add_or_remove_items'        => __( 'Add or remove skills', 'textdomain' ),
        'choose_from_most_used'      => __( 'Choose from the most used skills', 'textdomain' ),
        'menu_name'                  => __( 'Skills', 'textdomain' ),
    );

    $args_skill = array(
        'hierarchical'      => false, // FALSE = Tag style (Input field)
        'labels'            => $labels_skill,
        'show_ui'           => true,
        'show_admin_column' => true,
        'query_var'         => true,
        'rewrite'           => array( 'slug' => 'skill' ),
        'show_in_rest'      => true, // REQUIRED for Block Editor
    );

    register_taxonomy( 'skill', array( 'portfolio' ), $args_skill );
}
add_action( 'init', 'my_register_project_taxonomies', 0 );
```

## 3. Key Arguments

### `show_in_rest` (Crucial)
Just like with CPTs, setting this to `true` exposes the taxonomy to the REST API.
*   **True:** The taxonomy appears in the Document Sidebar in the Block Editor.
*   **False:** The taxonomy is hidden from the Block Editor (only visible in Quick Edit or Classic Editor).

### `show_admin_column`
If `true`, WordPress creates a column in the main Admin Post List (`/wp-admin/edit.php?post_type=portfolio`) showing the terms assigned to each post. This is highly recommended for usability.

## 4. FSE Templates for Taxonomies

Once registered, you can create specific templates for these archives in the Site Editor.

*   **URL:** `example.com/project-type/web-design/`
*   **Template File:** `taxonomy-project_type.html`
*   **Generic Fallback:** `archive.html`

To create a specific template visually:
1.  Go to **Appearance > Editor > Templates**.
2.  Click **Add New**.
3.  Select **Category & Taxonomy**.
4.  Select your custom taxonomy (**Project Types** or **Skills**).