WooCommerce Extension Development

Model note: Complex — payment gateways, HPOS compatibility, and block cart/checkout require multi-file reasoning. Use sonnet or opus. haiku for isolated CRUD or hook lookups only.

Guide for building WooCommerce extensions: custom product types, payment gateways, hooks, CRUD, REST, and admin UI. Assumes the host plugin passes the wp-plugin-audit baseline and the official wp-plugin-development security conventions.

When to use

• "Add a custom product type", "create a payment gateway", "add a shipping method".
• "Extend the WooCommerce REST API", "add fields to WC orders/products".
• "Build a WooCommerce admin tab", "add product meta", "custom checkout field".
• "Hook into WC cart/checkout", "add a fee", "apply a discount programmatically".
• "Debug WooCommerce order status flow", "fix a WC hook not firing".

Not for: General WordPress plugin architecture — use wp-plugin-development. PHPStan types for WC — use wp-phpstan-stubs to scaffold WC stubs.

Method

1. Identify extension point category

Determine which WC subsystem applies before writing code:

2. CRUD — use WC classes, not direct $wpdb

Always use WC CRUD methods; they fire the correct hooks and invalidate caches.

// Orders
$order = wc_create_order( [ 'status' => 'pending', 'customer_id' => $user_id ] );
$order->add_product( wc_get_product( $product_id ), 1 );
$order->calculate_totals();
$order->save();

// Products
$product = new WC_Product_Simple();
$product->set_name( 'My Product' );
$product->set_regular_price( '19.99' );
$product->set_status( 'publish' );
$product->save();

// Reading
$order   = wc_get_order( $order_id );       // returns WC_Order or false
$product = wc_get_product( $product_id );   // returns WC_Product subclass or false

For meta, use $order->get_meta() / $order->update_meta_data() + $order->save() — never update_post_meta() on orders (breaks HPOS).

3. HPOS compatibility

WooCommerce 8.2+ ships High-Performance Order Storage (HPOS). Extensions must declare compatibility or they're disabled in HPOS stores.

add_action( 'before_woocommerce_init', function() {
    if ( class_exists( \Automattic\WooCommerce\Utilities\FeaturesUtil::class ) ) {
        \Automattic\WooCommerce\Utilities\FeaturesUtil::declare_compatibility(
            'custom_order_tables', __FILE__, true
        );
    }
} );

Rules under HPOS:

• Never read/write orders via get_post_meta() / update_post_meta() — use WC_Order getters/setters.
• Never query orders via WP_Query with post_type=shop_order — use wc_get_orders().
• Avoid $wpdb queries directly on {prefix}posts for order data.

4. Payment gateway skeleton

class My_Payment_Gateway extends WC_Payment_Gateway {
    public function __construct() {
        $this->id                 = 'my_gateway';
        $this->method_title       = __( 'My Gateway', 'my-plugin' );
        $this->method_description = __( 'Pay via My Gateway.', 'my-plugin' );
        $this->supports           = [ 'products', 'refunds' ];
        $this->init_form_fields();
        $this->init_settings();
        $this->title   = $this->get_option( 'title' );
        $this->enabled = $this->get_option( 'enabled' );
        add_action( 'woocommerce_update_options_payment_gateways_' . $this->id,
            [ $this, 'process_settings' ] );
    }

    public function process_payment( $order_id ) {
        $order = wc_get_order( $order_id );
        // ... call payment API ...
        $order->payment_complete( $transaction_id );
        return [ 'result' => 'success', 'redirect' => $this->get_return_url( $order ) ];
    }

    public function process_refund( $order_id, $amount = null, $reason = '' ) {
        // return true on success, WP_Error on failure
    }
}
add_filter( 'woocommerce_payment_gateways', fn( $gateways ) => [ ...$gateways, My_Payment_Gateway::class ] );

5. REST API extension

Extend existing WC REST endpoints via woocommerce_rest_prepare_* hooks, or register a custom controller:

// Add field to products REST response
add_filter( 'woocommerce_rest_prepare_product_object', function( $response, $product, $request ) {
    $response->data['my_custom_field'] = $product->get_meta( '_my_field' );
    return $response;
}, 10, 3 );

// Accept field on write
add_filter( 'woocommerce_rest_pre_insert_product_object', function( $product, $request ) {
    if ( isset( $request['my_custom_field'] ) ) {
        $product->update_meta_data( '_my_field', sanitize_text_field( $request['my_custom_field'] ) );
    }
    return $product;
}, 10, 2 );

6. Key hooks reference

// Cart
add_action( 'woocommerce_cart_calculate_fees', [ $this, 'add_fee' ] );
add_filter( 'woocommerce_cart_item_price',     [ $this, 'modify_price' ], 10, 3 );

// Checkout
add_filter( 'woocommerce_checkout_fields',     [ $this, 'add_field' ] );
add_action( 'woocommerce_checkout_update_order_meta', [ $this, 'save_field' ] );

// Orders
add_action( 'woocommerce_order_status_changed', [ $this, 'on_status_change' ], 10, 4 );
add_filter( 'wc_order_statuses',               [ $this, 'register_status' ] );

// Products
add_filter( 'woocommerce_product_data_tabs',   [ $this, 'add_tab' ] );
add_action( 'woocommerce_product_data_panels', [ $this, 'render_panel' ] );
add_action( 'woocommerce_process_product_meta', [ $this, 'save_meta' ] );

7. Blocks (cart/checkout) compatibility

Classic shortcode hooks (woocommerce_checkout_fields) do not fire for the block-based checkout. Use the Store API extension registry:

add_action( 'woocommerce_blocks_loaded', function() {
    if ( ! function_exists( 'woocommerce_store_api_register_endpoint_data' ) ) return;
    woocommerce_store_api_register_endpoint_data( [
        'endpoint'        => Automattic\WooCommerce\StoreApi\Schemas\V1\CartSchema::IDENTIFIER,
        'namespace'       => 'my-plugin',
        'schema_callback' => fn() => [ 'my_field' => [ 'type' => 'string' ] ],
        'data_callback'   => fn() => [ 'my_field' => get_user_meta( get_current_user_id(), '_my_field', true ) ],
    ] );
} );

Declare blocks compatibility alongside HPOS:

\Automattic\WooCommerce\Utilities\FeaturesUtil::declare_compatibility( 'cart_checkout_blocks', __FILE__, true );

Notes

• Always check class_exists( 'WooCommerce' ) before any WC code; gate with woocommerce_loaded action.
• Minimum WC version requirements: HPOS stable in 8.2, blocks checkout stable in 8.3.
• Use wc_get_logger() for debug logging — writes to WooCommerce → Status → Logs, not the WP debug log.
• For testing: WC ships test helpers in woocommerce/tests/legacy/includes/ — use WC_Helper_Product::create_simple_product() etc. in PHPUnit tests.

References

• references/wc-hooks.md — categorised hook list (cart, checkout, orders, products, admin) with signatures and since versions.
• references/hpos-migration.md — HPOS compatibility checklist and query migration patterns.
• references/product-crud.md — WC_Product factory, meta CRUD, product type registration, variation patterns.
• references/rest-api.md — WC REST API auth, endpoints, batch operations, extending product/order responses via filters.
• references/block-cart-checkout.md — SlotFills, registerCheckoutFilters, extensionCartUpdate, woocommerce_store_api_register_update_callback, enqueue pattern.
• references/payment-methods.md — registerPaymentMethod(), registerExpressPaymentMethod(), AbstractPaymentMethodType PHP class, block payment registration.
• references/payment-gateway.md — WC_Payment_Gateway scaffold, process_payment(), process_refund(), webhook handler, settings fields.
• references/shipping.md — WC_Shipping_Method scaffold, calculate_shipping(), woocommerce_package_rates filter, zone handling, split packages.
• references/orders.md — wc_get_orders(), getter list, line item iteration, status hooks, custom status registration, wc_create_refund(), HPOS admin columns.
• references/coupons-tax-webhooks.md — WC_Coupon CRUD, wc_order_statuses filter, WC_Tax::calc_tax(), WC_Webhook programmatic creation, HMAC-SHA256 verification.