WooCommerce Extension / Plugin Development

Before writing code

Fetch live docs:

1. Fetch https://developer.wordpress.org/plugins/ for WordPress Plugin Handbook
2. Fetch https://developer.woocommerce.com/docs/extension-guidelines/ for WooCommerce extension guidelines
3. Web-search site:developer.woocommerce.com extension development best practices for current patterns

Main Plugin File

Required Headers

<?php
/**
 * Plugin Name: My WooCommerce Extension
 * Plugin URI:  https://example.com/my-extension
 * Description: A WooCommerce extension that does X.
 * Version:     1.0.0
 * Author:      Your Name
 * Author URI:  https://example.com
 * License:     GPL-2.0-or-later
 * Text Domain: my-woo-extension
 * Domain Path: /languages
 * Requires at least: 6.4
 * Requires PHP: 8.0
 * Requires Plugins: woocommerce
 * WC requires at least: 8.0
 * WC tested up to: 9.5
 */

Guarding Against Direct Access

Every PHP file starts with: defined( 'ABSPATH' ) || exit;

WooCommerce Dependency Check

Before initializing, verify WooCommerce is active:

• Check class_exists( 'WooCommerce' ) in a plugins_loaded hook
• Or use Requires Plugins: woocommerce header (WordPress 6.5+)

Activation & Deactivation

Activation Hook

register_activation_hook( __FILE__, 'my_plugin_activate' ) — runs on first activation:

• Create custom database tables (via dbDelta())
• Add default options (add_option())
• Schedule recurring actions (Action Scheduler)
• Flush rewrite rules if registering custom post types

Deactivation Hook

register_deactivation_hook( __FILE__, 'my_plugin_deactivate' ) — runs when deactivated:

• Unschedule cron/Action Scheduler events
• Flush rewrite rules
• Do NOT delete data (that's for uninstall)

Uninstall

Use uninstall.php (preferred) or register_uninstall_hook():

• Delete custom options, transients, custom tables
• Clean up user meta, post meta
• Only runs when user explicitly deletes the plugin

Custom Database Tables

Using $wpdb and dbDelta()

Create tables on activation:

• Use $wpdb->prefix for table name prefix
• Define schema with dbDelta() from wp-admin/includes/upgrade.php
• dbDelta() is idempotent — handles CREATE and ALTER
• Store DB version in an option to manage schema upgrades

Table Naming

Convention: {$wpdb->prefix}wc_my_extension_tablename

Autoloading

Composer PSR-4

Standard approach for namespaced classes:

• Configure autoload.psr-4 in composer.json
• require __DIR__ . '/vendor/autoload.php' in main plugin file
• Namespace convention: MyVendor\MyExtension\

WordPress File-Based

Legacy approach: require_once individual files in an includes/ directory. Still common in WooCommerce core.

Plugin Architecture Patterns

Singleton Main Class

Common WooCommerce extension pattern:

• Private constructor
• Static instance() method
• init() method that registers all hooks
• Accessed via global function (e.g., my_extension())

Service Container (Advanced)

For larger extensions, use a lightweight DI container or service provider pattern with constructor injection.

Feature Flags

Use WooCommerce's FeaturesUtil to declare compatibility:

• custom_order_tables — HPOS support
• cart_checkout_blocks — Block checkout support

Coding Standards

WordPress Coding Standards (WPCS)

• Tabs for indentation (not spaces)
• Yoda conditions: if ( 'value' === $var )
• Braces on same line for functions/control structures
• Spaces inside parentheses: if ( $condition )
• Prefix all globals: functions, classes, hooks, options, constants
• Escaping all output: esc_html(), esc_attr(), esc_url(), wp_kses()
• Sanitizing all input: sanitize_text_field(), absint(), wp_unslash()
• Nonces for all form submissions and AJAX

Best Practices

• Use Requires Plugins: woocommerce header (WordPress 6.5+)
• Declare HPOS compatibility in every extension
• Use Composer autoloading for new code
• Prefix everything to avoid naming collisions
• Internationalize all user-facing strings with __(), _e(), esc_html__()
• Load text domain via load_plugin_textdomain()
• Use WordPress built-in functions over raw PHP equivalents (wp_remote_get() vs curl)
• Never modify WooCommerce core files — always use hooks

Fetch the WordPress Plugin Handbook and WooCommerce extension guidelines for exact patterns and current requirements before implementing.