Wp Plugin Development

WordPress plugin development

When to use

Use this skill when:

• Creating a new WordPress plugin from scratch
• Preparing a plugin for submission to wordpress.org
• Structuring plugin files and folders
• Implementing activation, deactivation, or uninstall routines
• Building admin settings pages with the Settings API
• Registering custom post types or taxonomies
• Creating custom database tables
• Making a plugin translation-ready
• Handling plugin dependencies (required plugins or PHP extensions)
• Reviewing code before wordpress.org submission

Core development principles

The plugin development mantra

Use WordPress APIs, never reinvent the wheel
Prefix everything, conflict with nothing
Clean up after yourself on uninstall
Leave no trace when disabled

Key concepts

1. Prefix everything: All functions, classes, constants, and options must use a unique prefix to avoid conflicts
2. WordPress APIs first: Use WordPress functions over native PHP whenever an API exists
3. Lifecycle awareness: Know what runs on activation, deactivation, and uninstall — and keep them separate
4. Settings API: Never save options by hand; use the Settings API to register, validate, and store settings
5. GPL compatibility: All code and bundled libraries must be GPL-compatible for wordpress.org
6. No inline assets: Never print or tags directly with PHP — always use wp_enqueue_script() and wp_enqueue_style() with external files

Prefixing rules

All functions, classes, constants, hooks, options, post types, taxonomy slugs, and script/style handles must use a unique prefix of at least 4 characters. The Plugin Review Team rejects plugins with short or generic prefixes.

Do not use wp_, wordpress_, or wc_ as prefixes — these are reserved by WordPress core and WooCommerce.

Prefix consistency

A unique prefix of 4+ characters is not enough on its own: the same prefix must be used across every identifier in the plugin. The Plugin Review Team counts how many identifiers use the dominant prefix and flags any outlier — even if the outlier is itself a valid 4-character prefix.

// WRONG: 28 identifiers use ayudawp_*, one uses Aeuw_* → flagged.
class Aeuw_Promo_Banner { ... }

function ayudawp_register_settings() { ... }
function ayudawp_render_form() { ... }
add_option( 'ayudawp_settings', ... );

// CORRECT: every identifier uses the same dominant prefix.
class Ayudawp_Promo_Banner { ... }

function ayudawp_register_settings() { ... }
function ayudawp_render_form() { ... }
add_option( 'ayudawp_settings', ... );

Class file names should follow the same convention: class-ayudawp-promo-banner.php, not class-aeuw-promo-banner.php. The file slug must match the class name in lowercase, with dashes between words.

This applies to function names, class names, constants, options, transients, meta keys, post type slugs, taxonomy slugs, capability names, hook names, script/style handles, AJAX action names, and CSS class prefixes used inside the plugin's own markup.

Plugin file structure

A well-organized plugin is easier to review, maintain, and extend.

Recommended structure

my-plugin/
├── my-plugin.php           # Main plugin file (bootstrap only)
├── readme.txt              # wordpress.org readme (required)
├── uninstall.php           # Uninstall logic (alternative to hook)
├── assets/
│   ├── css/
│   │   ├── admin.css
│   │   └── public.css
│   ├── js/
│   │   ├── admin.js
│   │   └── public.js
│   └── images/
├── includes/
│   ├── class-my-plugin.php         # Main plugin class
│   ├── class-my-plugin-admin.php   # Admin-specific functionality
│   ├── class-my-plugin-public.php  # Public-facing functionality
│   ├── class-my-plugin-cpt.php     # Custom post types / taxonomies
│   ├── class-my-plugin-db.php      # Custom database tables
│   └── class-my-plugin-settings.php # Settings API implementation

Main plugin file

The main file is a bootstrap: it defines constants, checks requirements, and loads the rest.

<?php
/**
 * Plugin Name:       My Plugin
 * Plugin URI:        https://example.com/my-plugin
 * Description:       A brief description of what the plugin does.
 * Version:           1.0.0
 * Requires at least: 6.0
 * Requires PHP:      7.4
 * Author:            Your Name
 * Author URI:        https://example.com
 * License:           GPL-2.0-or-later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 * Text Domain:       my-plugin
 */

// Prevent direct file access.
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

// Plugin constants.
define( 'MYPLUGIN_VERSION',     '1.0.0' );
define( 'MYPLUGIN_FILE',        __FILE__ );
define( 'MYPLUGIN_DIR',         plugin_dir_path( __FILE__ ) );
define( 'MYPLUGIN_URL',         plugin_dir_url( __FILE__ ) );
define( 'MYPLUGIN_BASENAME',    plugin_basename( __FILE__ ) );

// Minimum requirements check.
function myplugin_meets_requirements() {
    if ( version_compare( PHP_VERSION, '7.4', '<' ) ) {
        return false;
    }
    if ( version_compare( get_bloginfo( 'version' ), '6.0', '<' ) ) {
        return false;
    }
    return true;
}

if ( ! myplugin_meets_requirements() ) {
    add_action( 'admin_notices', 'myplugin_requirements_notice' );
    return;
}

function myplugin_requirements_notice() {
    echo '<div class="notice notice-error"><p>' .
        esc_html__( 'My Plugin requires PHP 7.4+ and WordPress 6.0+.', 'my-plugin' ) .
        '</p></div>';
}

// Load the plugin.
require_once MYPLUGIN_DIR . 'includes/class-my-plugin.php';

// Lifecycle hooks must be registered in the main file, not inside a class.
register_activation_hook( MYPLUGIN_FILE,   array( 'My_Plugin', 'activate' ) );
register_deactivation_hook( MYPLUGIN_FILE, array( 'My_Plugin', 'deactivate' ) );

// Kick off.
My_Plugin::get_instance();

Escaping helpers in your admin JavaScript

Any script that builds HTML by concatenation needs an escaping helper, and the helper is part of the plugin's architecture, not a detail of one file. Decide it once, at the start, because retrofitting it later means auditing every call site.

// This does NOT encode quotes. Correct for text, unsafe inside an attribute.
function escHtml( s ) {
    var d = document.createElement( 'div' );
    d.textContent = s;
    return d.innerHTML;
}

// This does. Safe in any position.
function escAttr( s ) {
    if ( s === null || typeof s === 'undefined' ) { return ''; }
    return String( s )
        .replace( /&/g, '&amp;' ).replace( /</g, '&lt;' ).replace( />/g, '&gt;' )
        .replace( /"/g, '&quot;' ).replace( /'/g, '&#039;' );
}

Two conventions that prevent the whole class of bug:

• Either a single helper that is safe in attribute position, or two with explicit names. A lone escapeHtml() used both inside <td> and inside value="…" is a bug waiting for its context.
• Pick the helper by the output context, not by trusting the origin. A translated label inside an attribute goes through escAttr() just like user data, because what changes over time is who calls the renderer, not what the renderer escapes.

See the security skill for the full reasoning; this is the architectural half of it.

Asset loading rules

WordPress plugins must load all JavaScript and CSS through the enqueue API using external files. Printing <script> or <style> tags directly in PHP output is forbidden — it bypasses WordPress dependency management, breaks Content Security Policy headers, prevents caching and deduplication, and is flagged by the Plugin Review Team.

// WRONG: Inline script printed with PHP
add_action( 'wp_head', 'myplugin_bad_inline_script' );
function myplugin_bad_inline_script() {
    echo '<script>var config = { api: "https://example.com" };</script>';
}

// WRONG: Inline style printed with PHP
add_action( 'wp_head', 'myplugin_bad_inline_style' );
function myplugin_bad_inline_style() {
    echo '<style>.my-widget { color: red; }</style>';
}

// CORRECT: External JS file with data passed via wp_localize_script
wp_enqueue_script(
    'myplugin-frontend',
    MYPLUGIN_URL . 'assets/js/frontend.js',
    array(),
    MYPLUGIN_VERSION,
    true
);
wp_localize_script( 'myplugin-frontend', 'mypluginConfig', array(
    'api' => 'https://example.com',
) );

// CORRECT: External CSS file
wp_enqueue_style(
    'myplugin-frontend',
    MYPLUGIN_URL . 'assets/css/frontend.css',
    array(),
    MYPLUGIN_VERSION
);

// CORRECT: Small dynamic CSS via wp_add_inline_style (requires a registered stylesheet)
$custom_color = sanitize_hex_color( get_option( 'myplugin_color', '#333' ) );
wp_add_inline_style( 'myplugin-frontend', ".myplugin-widget { color: {$custom_color}; }" );

// CORRECT: Small dynamic JS via wp_add_inline_script (requires a registered script)
wp_add_inline_script( 'myplugin-frontend', 'console.log("loaded");', 'after' );

The only acceptable way to add small amounts of dynamic CSS or JS is through wp_add_inline_style() and wp_add_inline_script(), which attach the code to a properly enqueued handle.

Plugin header requirements for wordpress.org

Plugin lifecycle

Activation hook

Runs when the plugin is activated. Use it to create database tables, set default options, and schedule cron events.

Careful with anything you write outside your own tables and options. Activation runs with activate_plugins, which on a multisite network the network administrator can delegate to every subsite administrator with a native checkbox (Network Settings, Menu Settings, Plugins). If activation writes wp-config.php, the root .htaccess or the root robots.txt, one site is rewriting what the whole network reads, and the plugin may not even be active on the sites that suffer it. Gate those writes with is_multisite() ? current_user_can( 'manage_network_options' ) : current_user_can( 'manage_options' ), and prefer the virtual route when WordPress offers one: the robots_txt filter is per site, the physical file is not.

// CORRECT: Activation - set up what the plugin needs to run
public static function activate() {
    // Check capabilities - prevents direct URL activation exploits
    if ( ! current_user_can( 'activate_plugins' ) ) {
        return;
    }

    // Create custom tables
    self::create_tables();

    // Set default options (only if they don't exist yet)
    if ( false === get_option( 'myplugin_settings' ) ) {
        add_option( 'myplugin_settings', array(
            'enabled' => true,
            'limit'   => 10,
        ), '', 'yes' ); // 'yes' = autoload
    }

    // Schedule cron events
    if ( ! wp_next_scheduled( 'myplugin_daily_task' ) ) {
        wp_schedule_event( time(), 'daily', 'myplugin_daily_task' );
    }

    // Store plugin version for future upgrade checks
    update_option( 'myplugin_version', MYPLUGIN_VERSION );

    // Flush rewrite rules if registering CPTs
    flush_rewrite_rules();
}

// WRONG: Never run heavy logic or queries during activation without guards
public static function activate() {
    $results = $wpdb->get_results( "SELECT * FROM {$wpdb->posts}" ); // Never!
    wp_remote_get( 'https://api.example.com/register' ); // Never!
}

Deactivation hook

Runs when the plugin is deactivated. Clean up temporary data and scheduled events. Do NOT delete user data here.

// CORRECT: Deactivation - stop scheduled tasks, clear transients
public static function deactivate() {
    if ( ! current_user_can( 'activate_plugins' ) ) {
        return;
    }

    // Remove scheduled cron events
    wp_clear_scheduled_hook( 'myplugin_daily_task' );

    // Clear transients
    delete_transient( 'myplugin_cache' );

    // Flush rewrite rules (remove CPT slugs from .htaccess)
    flush_rewrite_rules();

    // WRONG: Do NOT delete options or tables here - that is uninstall logic
}

Uninstall logic

Runs only when the user deletes the plugin. This is where you permanently remove all plugin data.

// OPTION A: uninstall.php in the plugin root (recommended for complex cleanup)
<?php
// Prevent direct access
if ( ! defined( 'WP_UNINSTALL_PLUGIN' ) ) {
    exit;
}

// Delete options
delete_option( 'myplugin_settings' );
delete_option( 'myplugin_version' );

// Delete user meta
delete_metadata( 'user', 0, 'myplugin_preference', '', true );

// Drop custom tables
global $wpdb;
$wpdb->query( "DROP TABLE IF EXISTS {$wpdb->prefix}myplugin_data" );

// Delete all plugin transients
$wpdb->query(
    "DELETE FROM {$wpdb->options}
     WHERE option_name LIKE '\_transient\_myplugin\_%'
     OR option_name LIKE '\_transient\_timeout\_myplugin\_%'"
);

// OPTION B: register_uninstall_hook() in main file (for simple cleanup only)
// register_uninstall_hook( MYPLUGIN_FILE, 'myplugin_uninstall' );
// Note: uninstall.php takes precedence over register_uninstall_hook()

Path detection in uninstall.php

The Plugin Review Team flags any combination of WP_PLUGIN_DIR with a hardcoded slug literal as "hardcoded plugin folder path". It does not matter if the code is conceptually correct (e.g. detecting a legacy parallel install); the reviewer will reject it.

// REJECTED: even though it would work, the linter flags the slug literal.
$canonical = trailingslashit( WP_PLUGIN_DIR ) . 'my-plugin';
if ( __DIR__ !== untrailingslashit( $canonical ) && is_dir( $canonical ) ) {
    return;
}

// ACCEPTED: derive the path from __FILE__ instead.
$plugin_dir = plugin_dir_path( __FILE__ );   // or use __DIR__

If you genuinely need a safeguard for legacy installation folders (e.g. users who downloaded a GitHub source ZIP before the canonical wordpress.org release existed), document the upgrade path in the FAQ instead and let the standard install/uninstall flow handle it.

Lifecycle comparison

Defaults are product decisions, and sometimes security decisions

The value a plugin ships with is the value almost every install will run forever. Two consequences that are easy to miss:

• A protection that ships disabled protects nobody. In one audited plugin the correct reverse-DNS verification of search engine bots was written, working and switched off by default, while the feature it was supposed to secure was switched on: the "private site" mode opened for anyone sending User-Agent: Googlebot. The code was right, the default was the vulnerability.
• Changing a default does not reach existing installs. If activation persisted the whole defaults array into an option, wp_parse_args() will never restore the new value, because the old one is stored. The change only affects fresh installs unless you migrate.

// Migrate with a version option, never with a transient: a transient expires and
// the routine runs again, which is how a user's deliberate choice gets overwritten.
if ( (int) get_option( 'myplugin_settings_version', 0 ) < 2 ) {
    $settings = get_option( 'myplugin_settings', array() );
    if ( is_array( $settings ) && empty( $settings['verify_bots'] ) ) {
        $settings['verify_bots'] = true;
        update_option( 'myplugin_settings', $settings );
    }
    update_option( 'myplugin_settings_version', 2 );
}

Say it in the changelog too. A default that flips is a behaviour change, and users who relied on the old one deserve to read about it before they update rather than after.

Main plugin class

Use a singleton to avoid multiple instantiations and keep global state controlled.

<?php
// Prevent direct access.
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

/**
 * Main plugin class.
 */
class My_Plugin {

    /** @var My_Plugin|null Singleton instance */
    private static $instance = null;

    /**
     * Get or create the singleton instance.
     */
    public static function get_instance(): self {
        if ( null === self::$instance ) {
            self::$instance = new self();
        }
        return self::$instance;
    }

    /**
     * Private constructor - use get_instance().
     */
    private function __construct() {
        $this->load_dependencies();
        $this->define_hooks();
    }

    /**
     * Load required files.
     */
    private function load_dependencies(): void {
        require_once MYPLUGIN_DIR . 'includes/class-my-plugin-admin.php';
        require_once MYPLUGIN_DIR . 'includes/class-my-plugin-public.php';
        require_once MYPLUGIN_DIR . 'includes/class-my-plugin-cpt.php';
    }

    /**
     * Register all action and filter hooks.
     */
    private function define_hooks(): void {
        $admin  = new My_Plugin_Admin();
        $public = new My_Plugin_Public();
        $cpt    = new My_Plugin_CPT();

        // Admin hooks
        add_action( 'admin_menu',            array( $admin, 'add_admin_menu' ) );
        add_action( 'admin_init',            array( $admin, 'register_settings' ) );
        add_action( 'admin_enqueue_scripts', array( $admin, 'enqueue_assets' ) );

        // Public hooks
        add_action( 'wp_enqueue_scripts', array( $public, 'enqueue_assets' ) );
        add_shortcode( 'my_plugin',       array( $public, 'render_shortcode' ) );

        // CPT and taxonomy registration
        add_action( 'init', array( $cpt, 'register_post_types' ) );
        add_action( 'init', array( $cpt, 'register_taxonomies' ) );
    }

    /**
     * Activation callback (called from register_activation_hook in main file).
     */
    public static function activate(): void {
        // Activation logic here
        flush_rewrite_rules();
    }

    /**
     * Deactivation callback.
     */
    public static function deactivate(): void {
        wp_clear_scheduled_hook( 'myplugin_daily_task' );
        flush_rewrite_rules();
    }
}

Hooks system

Actions vs filters

// ACTION: do something at a point in execution (no return value needed)
add_action( 'save_post', 'myplugin_on_save_post', 10, 2 );
function myplugin_on_save_post( int $post_id, WP_Post $post ): void {
    // Do something when a post is saved
}

// FILTER: modify a value and return it (always return the value!)
add_filter( 'the_content', 'myplugin_filter_content', 10, 1 );
function myplugin_filter_content( string $content ): string {
    // Modify and always return
    return $content . '<p>Added by plugin</p>';
}

// WRONG: Forgetting to return in a filter breaks the site
add_filter( 'the_content', function( $content ) {
    echo $content; // Never echo in a filter!
    // No return = null is returned, content disappears
} );

Hook priorities

// Default priority is 10. Lower = earlier, higher = later.
add_action( 'init', 'myplugin_early_init', 5 );   // Runs before default
add_action( 'init', 'myplugin_normal_init' );       // Priority 10 (default)
add_action( 'init', 'myplugin_late_init', 20 );    // Runs after default

// Number of accepted arguments (4th parameter)
add_action( 'save_post', 'myplugin_handler', 10, 3 ); // $post_id, $post, $update

Removing hooks

// To remove a hook added with a named function
remove_action( 'wp_head', 'wp_generator' );

// To remove a hook added with a class method - needs same instance
$instance = My_Plugin::get_instance();
remove_action( 'init', array( $instance, 'some_method' ) );

// WRONG: This does not work for anonymous functions (no reference)
$fn = function() { /* ... */ };
add_action( 'init', $fn );
remove_action( 'init', $fn ); // Works only if $fn is still in scope

Filters that depend on a specific call site

Some filters only fire in a specific code path. The most common pitfall: shortcode_atts_{tag} only fires when WordPress calls shortcode_atts() from inside do_shortcode(). If the same render function is invoked directly from another context (a custom WooCommerce endpoint, a Gutenberg block render callback, a REST response, an admin_post_* handler), the filter never runs.

// WRONG: The filter only applies when the form is rendered via [my_form] shortcode.
// Calling my_render_form() from a WC endpoint silently skips the prefill.
add_filter( 'shortcode_atts_my_form', 'my_prefill_from_query' );
function my_prefill_from_query( $atts ) {
    if ( isset( $_GET['order_id'] ) ) {
        $atts['order_id'] = sanitize_text_field( wp_unslash( $_GET['order_id'] ) );
    }
    return $atts;
}

// CORRECT: Extract the logic to a helper that both call sites invoke.
function my_get_prefill_order_id() {
    // ... nonce check + sanitize + return value ...
    return $order_id;
}

// Endpoint caller passes the value directly:
function my_account_endpoint_content() {
    my_render_form( array(
        'order_id' => my_get_prefill_order_id(),
    ) );
}

// Shortcode caller goes through the filter, which uses the same helper:
add_filter( 'shortcode_atts_my_form', function( $atts ) {
    $order_id = my_get_prefill_order_id();
    if ( '' !== $order_id ) {
        $atts['order_id'] = $order_id;
    }
    return $atts;
} );

Same pattern applies to any filter named after a specific hook context: the_content filters do not run on raw post body access, the_title does not run on get_the_title() in some admin contexts, etc. When in doubt, extract the logic and call it from every entry point.

Settings API

The Settings API handles validation, storage, and security for plugin options. Never save options manually with $_POST.

And remember what a saved option can trigger. Hooking update_option_<name> to write a file is a common and useful pattern, but the option is per site while the file may not be. On a network, an administrator of any subsite saving their own settings can rewrite the root .htaccess or robots.txt that every site serves, with no capability beyond manage_options. If a save writes anything shared, gate it, tell the user why the control is unavailable instead of failing silently, and consider not registering the hook at all on subsites.

Complete Settings API implementation

<?php
// Prevent direct access.
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

/**
 * Handles plugin settings using the WordPress Settings API.
 */
class My_Plugin_Settings {

    /** @var string Option name in wp_options */
    const OPTION_NAME = 'myplugin_settings';

    /** @var string Settings page slug */
    const PAGE_SLUG = 'myplugin-settings';

    /** @var string Settings group (must match register_setting) */
    const OPTION_GROUP = 'myplugin_options_group';

    /**
     * Register settings, sections, and fields.
     * Hooked to admin_init.
     */
    public function register(): void {
        // Register the option with a sanitize callback
        register_setting(
            self::OPTION_GROUP,
            self::OPTION_NAME,
            array(
                'sanitize_callback' => array( $this, 'sanitize_settings' ),
                'default'           => $this->get_defaults(),
            )
        );

        // Add a section
        add_settings_section(
            'myplugin_general_section',
            __( 'General Settings', 'my-plugin' ),
            array( $this, 'render_general_section' ),
            self::PAGE_SLUG
        );

        // Add fields to the section
        add_settings_field(
            'myplugin_field_enabled',
            __( 'Enable feature', 'my-plugin' ),
            array( $this, 'render_field_enabled' ),
            self::PAGE_SLUG,
            'myplugin_general_section'
        );

        add_settings_field(
            'myplugin_field_limit',
            __( 'Results limit', 'my-plugin' ),
            array( $this, 'render_field_limit' ),
            self::PAGE_SLUG,
            'myplugin_general_section'
        );
    }

    /**
     * Sanitize all settings on save.
     * This is the only place where $_POST data is processed.
     *
     * @param  array $input Raw input from the form.
     * @return array Sanitized settings.
     */
    public function sanitize_settings( array $input ): array {
        $sanitized = $this->get_defaults();

        // Checkbox: present = true, absent = false
        $sanitized['enabled'] = isset( $input['enabled'] );

        // Integer with range validation
        if ( isset( $input['limit'] ) ) {
            $limit = absint( $input['limit'] );
            $sanitized['limit'] = ( $limit >= 1 && $limit <= 100 ) ? $limit : 10;
        }

        // Text field
        if ( isset( $input['api_key'] ) ) {
            $sanitized['api_key'] = sanitize_text_field( $input['api_key'] );
        }

        // Select with safelist validation
        $allowed_modes = array( 'simple', 'advanced' );
        if ( isset( $input['mode'] ) && in_array( $input['mode'], $allowed_modes, true ) ) {
            $sanitized['mode'] = $input['mode'];
        }

        return $sanitized;
    }

    /**
     * Get default settings values.
     */
    public function get_defaults(): array {
        return array(
            'enabled' => true,
            'limit'   => 10,
            'api_key' => '',
            'mode'    => 'simple',
        );
    }

    /**
     * Get a single setting value with fallback to default.
     *
     * @param  string $key Setting key.
     * @return mixed  Setting value.
     */
    public function get( string $key ) {
        $settings = get_option( self::OPTION_NAME, $this->get_defaults() );
        $defaults  = $this->get_defaults();
        return $settings[ $key ] ?? $defaults[ $key ] ?? null;
    }

    /**
     * Render the settings section description.
     */
    public function render_general_section(): void {
        echo '<p>' . esc_html__( 'Configure the general plugin behavior.', 'my-plugin' ) . '</p>';
    }

    /**
     * Render the "enabled" checkbox field.
     */
    public function render_field_enabled(): void {
        $value = $this->get( 'enabled' );
        printf(
            '<input type="checkbox" id="myplugin_field_enabled" name="%s[enabled]" value="1" %s>',
            esc_attr( self::OPTION_NAME ),
            checked( $value, true, false )
        );
        echo '<label for="myplugin_field_enabled">' .
             esc_html__( 'Enable the main feature', 'my-plugin' ) .
             '</label>';
    }

    /**
     * Render the "limit" number field.
     */
    public function render_field_limit(): void {
        $value = $this->get( 'limit' );
        printf(
            '<input type="number" id="myplugin_field_limit" name="%s[limit]" value="%d" min="1" max="100" class="small-text">',
            esc_attr( self::OPTION_NAME ),
            absint( $value )
        );
        echo '<p class="description">' .
             esc_html__( 'Number of results to show (1-100).', 'my-plugin' ) .
             '</p>';
    }
}

Admin menu and settings page

/**
 * Registers admin menu pages.
 * Hooked to admin_menu.
 */
public function add_admin_menu(): void {
    // Top-level menu page
    add_menu_page(
        __( 'My Plugin', 'my-plugin' ),         // Page title
        __( 'My Plugin', 'my-plugin' ),         // Menu title
        'manage_options',                         // Capability required
        'myplugin-settings',                     // Menu slug
        array( $this, 'render_settings_page' ), // Callback
        'dashicons-admin-generic',               // Icon
        80                                        // Position
    );

    // Submenu page (can also add submenus under existing menus)
    add_submenu_page(
        'myplugin-settings',                      // Parent slug
        __( 'My Plugin Settings', 'my-plugin' ), // Page title
        __( 'Settings', 'my-plugin' ),           // Menu title
        'manage_options',
        'myplugin-settings',
        array( $this, 'render_settings_page' )
    );
}

/**
 * Render the settings page.
 * settings_fields() and do_settings_sections() do all the heavy lifting.
 */
public function render_settings_page(): void {
    // Always check capabilities again before rendering
    if ( ! current_user_can( 'manage_options' ) ) {
        wp_die( esc_html__( 'You do not have permission to access this page.', 'my-plugin' ) );
    }
    ?>
    <div class="wrap">
        <h1><?php echo esc_html( get_admin_page_title() ); ?></h1>

        <?php settings_errors( 'myplugin_messages' ); ?>

        <form method="post" action="options.php">
            <?php
            // Output nonce, action, and option_page fields
            settings_fields( My_Plugin_Settings::OPTION_GROUP );

            // Output the registered sections and fields
            do_settings_sections( My_Plugin_Settings::PAGE_SLUG );

            submit_button( __( 'Save settings', 'my-plugin' ) );
            ?>
        </form>
    </div>
    <?php
}

Custom post types and taxonomies

Registering a custom post type

/**
 * Registers custom post types.
 * Hooked to init.
 */
public function register_post_types(): void {
    $labels = array(
        'name'               => _x( 'Events', 'post type general name', 'my-plugin' ),
        'singular_name'      => _x( 'Event', 'post type singular name', 'my-plugin' ),
        'menu_name'          => _x( 'Events', 'admin menu', 'my-plugin' ),
        'add_new'            => __( 'Add new', 'my-plugin' ),
        'add_new_item'       => __( 'Add new event', 'my-plugin' ),
        'edit_item'          => __( 'Edit event', 'my-plugin' ),
        'not_found'          => __( 'No events found.', 'my-plugin' ),
        'not_found_in_trash' => __( 'No events found in trash.', 'my-plugin' ),
    );

    $args = array(
        'labels'             => $labels,
        'public'             => true,
        'publicly_queryable' => true,
        'show_ui'            => true,
        'show_in_rest'       => true, // Required for Gutenberg support
        'menu_position'      => 5,
        'menu_icon'          => 'dashicons-calendar-alt',
        'supports'           => array( 'title', 'editor', 'thumbnail', 'excerpt' ),
        'has_archive'        => true,
        'rewrite'            => array( 'slug' => 'events' ),
        'capability_type'    => 'post',
    );

    register_post_type( 'myplugin_event', $args );
}

// IMPORTANT: Always flush rewrite rules on activation/deactivation when registering CPTs
// Do NOT call flush_rewrite_rules() directly on init - only on activation/deactivation

Registering a custom taxonomy

public function register_taxonomies(): void {
    $labels = array(
        'name'              => _x( 'Event Categories', 'taxonomy general name', 'my-plugin' ),
        'singular_name'     => _x( 'Event Category', 'taxonomy singular name', 'my-plugin' ),
        'search_items'      => __( 'Search event categories', 'my-plugin' ),
        'all_items'         => __( 'All event categories', 'my-plugin' ),
        'edit_item'         => __( 'Edit event category', 'my-plugin' ),
        'update_item'       => __( 'Update event category', 'my-plugin' ),
        'add_new_item'      => __( 'Add new event category', 'my-plugin' ),
        'not_found'         => __( 'No event categories found.', 'my-plugin' ),
    );

    register_taxonomy(
        'myplugin_event_cat',   // Taxonomy slug
        array( 'myplugin_event' ), // Post types it applies to
        array(
            'labels'            => $labels,
            'hierarchical'      => true,  // true = category-like, false = tag-like
            'public'            => true,
            'show_in_rest'      => true,  // Required for Gutenberg
            'show_admin_column' => true,
            'rewrite'           => array( 'slug' => 'event-category' ),
        )
    );
}

Custom database tables

Only create custom tables when WordPress's existing data structures (posts, meta, options) genuinely cannot serve the use case.

Creating tables with dbDelta

/**
 * Creates or updates the custom database table.
 * Uses dbDelta() which handles both CREATE and ALTER safely.
 */
public static function create_tables(): void {
    global $wpdb;

    $table_name      = $wpdb->prefix . 'myplugin_data';
    $charset_collate = $wpdb->get_charset_collate();

    // dbDelta requires specific formatting:
    // - Two spaces before field definitions
    // - PRIMARY KEY must be uppercase
    // - Each line ends with a comma (except the last field before the closing paren)
    $sql = "CREATE TABLE {$table_name} (
        id bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
        user_id bigint(20) UNSIGNED NOT NULL DEFAULT 0,
        post_id bigint(20) UNSIGNED NOT NULL DEFAULT 0,
        data longtext NOT NULL,
        status varchar(20) NOT NULL DEFAULT 'pending',
        created_at datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
        PRIMARY KEY  (id),
        KEY user_id (user_id),
        KEY post_id (post_id)
    ) {$charset_collate};";

    require_once ABSPATH . 'wp-admin/includes/upgrade.php';
    dbDelta( $sql );

    // Store the table version for future upgrades
    update_option( 'myplugin_db_version', '1.0' );
}

/**
 * Run table upgrades when plugin version changes.
 * Hook to plugins_loaded.
 */
public function maybe_upgrade(): void {
    $installed = get_option( 'myplugin_db_version', '0' );

    if ( version_compare( $installed, '1.1', '<' ) ) {
        global $wpdb;
        $table = $wpdb->prefix . 'myplugin_data';

        // dbDelta handles adding new columns safely
        $sql = "CREATE TABLE {$table} (
            id bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
            user_id bigint(20) UNSIGNED NOT NULL DEFAULT 0,
            post_id bigint(20) UNSIGNED NOT NULL DEFAULT 0,
            data longtext NOT NULL,
            status varchar(20) NOT NULL DEFAULT 'pending',
            priority tinyint(3) UNSIGNED NOT NULL DEFAULT 0,
            created_at datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
            PRIMARY KEY  (id),
            KEY user_id (user_id)
        ) {$wpdb->get_charset_collate()};";

        require_once ABSPATH . 'wp-admin/includes/upgrade.php';
        dbDelta( $sql );

        update_option( 'myplugin_db_version', '1.1' );
    }
}

dbDelta formatting rules

Internationalization

Every user-facing string must be wrapped in a localization function. This is mandatory for wordpress.org.

Localization functions

i18n examples

// CORRECT: All user-facing strings wrapped and escaped
echo '<h2>' . esc_html__( 'Plugin Settings', 'my-plugin' ) . '</h2>';

// CORRECT: Singular/plural
printf(
    /* translators: %d: number of items */
    esc_html( _n( '%d item found.', '%d items found.', $count, 'my-plugin' ) ),
    absint( $count )
);

// CORRECT: Context for disambiguation (same word, different meaning)
$label = _x( 'Draft', 'post status', 'my-plugin' );
$label = _x( 'Draft', 'button label', 'my-plugin' );

// CORRECT: Variable in translated string - use printf/sprintf, not concatenation
printf(
    /* translators: %s: user display name */
    esc_html__( 'Hello, %s!', 'my-plugin' ),
    esc_html( $user->display_name )
);

// WRONG: Concatenating strings breaks translation
echo esc_html__( 'Hello, ', 'my-plugin' ) . esc_html( $name ) . '!';

// WRONG: Translating variable content
$status = 'published';
echo esc_html__( $status, 'my-plugin' ); // Translators can't see this!

Text domain rules for wordpress.org

// CORRECT: Text domain is a string literal, matches plugin folder slug
__( 'text', 'my-plugin' );

// WRONG: Variable text domain - prevents string extraction
$domain = 'my-plugin';
__( 'text', $domain );

// The text domain in function calls MUST match the Text Domain header in the plugin file
// and the plugin folder name on wordpress.org

Translation template generation

There is no need to generate a .pot file because de use of Domain Path is deprecated

load_plugin_textdomain() is not needed since WordPress 4.6.

Plugin dependencies

Checking for required plugins

// CORRECT: Check on plugins_loaded (all plugins are loaded)
add_action( 'plugins_loaded', 'myplugin_check_dependencies' );

function myplugin_check_dependencies(): void {
    // Check if WooCommerce is active
    if ( ! class_exists( 'WooCommerce' ) ) {
        add_action( 'admin_notices', 'myplugin_woo_missing_notice' );
        // Optionally deactivate self
        deactivate_plugins( plugin_basename( MYPLUGIN_FILE ) );
        return;
    }

    // Check minimum WooCommerce version
    if ( defined( 'WC_VERSION' ) && version_compare( WC_VERSION, '7.0', '<' ) ) {
        add_action( 'admin_notices', 'myplugin_woo_version_notice' );
        return;
    }

    // All good - initialize the plugin
    My_Plugin::get_instance();
}

function myplugin_woo_missing_notice(): void {
    echo '<div class="notice notice-error"><p>' .
        sprintf(
            /* translators: %s: plugin name */
            esc_html__( 'My Plugin requires %s to be installed and active.', 'my-plugin' ),
            '<strong>WooCommerce</strong>'
        ) .
        '</p></div>';
}

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