WooCommerce Shipping Method Development

Before writing code

Fetch live docs:

1. Web-search site:developer.woocommerce.com shipping method api for shipping method guide
2. Web-search woocommerce custom shipping method tutorial for implementation patterns
3. Fetch https://woocommerce.github.io/code-reference/classes/WC-Shipping-Method.html for class reference

Shipping Architecture

Shipping Zones

Geographic regions that determine available shipping methods:

• Zone = set of geographic rules (countries, states, postcodes)
• Each zone has one or more shipping methods assigned
• "Locations not covered by your other zones" = default catch-all zone
• Zones are evaluated in order — first match wins

Shipping Classes

Product-level classification for rate customization:

• Assign products to shipping classes (e.g., "Heavy Items", "Fragile")
• Shipping methods can define different rates per class
• Managed in WooCommerce > Settings > Shipping > Shipping Classes

WC_Shipping_Method

Base Class

All custom shipping methods extend WC_Shipping_Method:

Registration

Filter woocommerce_shipping_methods:

add_filter( 'woocommerce_shipping_methods', function( $methods ) {
    $methods['my_shipping'] = 'My_Shipping_Method';
    return $methods;
});

Implementation Methods

Required Methods

• __construct( $instance_id ) — set $id, $method_title, $supports, initialize settings
• init_form_fields() — define settings fields (flat rate, per-item, per-class)
• calculate_shipping( $package ) — compute rates and add via $this->add_rate()

calculate_shipping()

Receives $package array containing:

• contents — cart items in this package
• destination — shipping address (country, state, postcode, city)
• cart_subtotal — package subtotal

Returns rates via $this->add_rate():

$this->add_rate( [
    'id'       => $this->get_rate_id(),
    'label'    => $this->title,
    'cost'     => $calculated_cost,
    'taxes'    => '', // empty = auto-calculate, 'false' = tax-free
    'calc_tax' => 'per_order', // or 'per_item'
    'package'  => $package,
]);

Instance Settings

For zone-based configuration (per-zone settings):

• Set $this->instance_form_fields instead of $this->form_fields
• Add 'instance-settings' and 'instance-settings-modal' to $this->supports
• Settings are stored per zone instance, not globally

Shipping Packages

What Packages Are

Cart items grouped for shipping calculation:

• Default: all items in one package
• Filter woocommerce_cart_shipping_packages to split items into multiple packages
• Each package is calculated independently (different rates for different groups of items)

Package Format

$package = [
    'contents'        => [ /* cart items */ ],
    'contents_cost'   => 50.00,
    'applied_coupons' => [],
    'destination'     => [
        'country'  => 'US',
        'state'    => 'CA',
        'postcode' => '90210',
        'city'     => 'Beverly Hills',
    ],
];

Rate Calculation Patterns

Flat Rate

Fixed cost regardless of cart contents. Optionally add per-item or per-class surcharges.

Weight-Based

Calculate from total package weight:

• Sum $item['data']->get_weight() * $item['quantity'] for all items
• Apply rate tiers (e.g., $5 for 0-1kg, $10 for 1-5kg)

Table Rate

Complex rate calculation based on combinations of weight, item count, destination, and price. Often implemented with rate tables stored in custom DB tables.

Live API Rates

Call carrier APIs (UPS, FedEx, USPS, DHL):

• Send package dimensions, weight, origin, destination
• Receive available services and rates
• Cache responses (transients) to avoid excessive API calls
• Handle API failures gracefully with fallback rates

Tracking

Adding Tracking Data

Store tracking info as order meta:

• $order->update_meta_data( '_tracking_number', $number )
• $order->update_meta_data( '_tracking_provider', $carrier )
• Display in order emails and My Account via hooks

Free Shipping

Built-in WC_Shipping_Free_Shipping — enable based on:

• Minimum order amount
• Coupon with free shipping
• Both (coupon AND minimum amount)

Best Practices

• Cache rate calculations (transients) for API-based methods
• Handle API failures with fallback/default rates
• Support shipping classes for per-product rate customization
• Use instance settings for per-zone configuration
• Validate destination before calculating rates
• Return multiple rate options when available (e.g., Standard, Express, Overnight)
• Add tracking support for customer transparency
• Test with various cart compositions (single item, multiple, heavy, virtual mix)

Fetch the WooCommerce shipping method documentation for exact method signatures, package format, and instance settings patterns before implementing.