checkoutwoocommerce

WooCommerce Custom Checkout Fields: Add and Save

November 2, 202611 min read·ShopMonitor Team

WooCommerce custom checkout fields are not finished when they appear on the page. They also have to survive submission, land on the order, and reject only data that would make fulfilment impossible. Miss the save hook and the customer completes checkout while the value disappears. Make validation too rigid and good orders fail at the last step.

This guide covers the full path with practical code, including the different rules for Checkout blocks and express payment buttons.

The woocommerce_checkout_fields Filter

On the classic checkout, this filter gives you the complete form as a nested array before WooCommerce renders it. Use it to change core fields.

Structure of the WooCommerce Checkout Fields Array

woocommerce_checkout_fields returns four top-level groups. Each group contains fields keyed by input name. Each field is an array of properties such as label, placeholder, required, class, priority, and validate.

The four field groups in $fields

Group	Holds	Rendered when
`billing`	Billing name, address, phone and email	Always
`shipping`	Shipping name and address	The cart needs shipping and the customer uses another address
`account`	Username and password fields	Account creation at checkout is enabled
`order`	Order notes and, by convention, your own order-level fields	Always, unless you remove it

Core priorities usually increase in tens, leaving useful gaps for your own fields.

Two boundaries catch experienced developers too. This filter affects only the classic checkout shortcode, not the Checkout block. It also controls rendering and required state only. Without a save hook, a field added here loses its value after checkout. After a WooCommerce update, confirm the field still renders and saves before you assume checkout is healthy.

A Minimal Working Example

Put this in a small site-specific plugin or child theme. Do not put it in a parent theme:

add_filter( 'woocommerce_checkout_fields', 'sm_checkout_fields' );

function sm_checkout_fields( $fields ) {
	$fields['billing']['billing_phone']['required'] = false;
	$fields['billing']['billing_phone']['label']    = 'Mobile number for delivery updates';
	$fields['order']['order_comments']['placeholder'] = 'Anything the courier should know';

	return $fields;
}

Always return $fields. A filter that returns nothing gives WooCommerce an empty checkout form and can take a live store offline.

Address fields also pass through woocommerce_billing_fields, woocommerce_shipping_fields, and woocommerce_default_address_fields. Use those hooks when the same change must apply to My Account address forms.

Removing and Reordering Existing Fields

Unset a key to drop a field, and set priority to move it:

add_filter( 'woocommerce_checkout_fields', 'sm_trim_checkout_fields' );

function sm_trim_checkout_fields( $fields ) {
	// Drop fields this store genuinely does not use.
	unset( $fields['billing']['billing_company'] );
	unset( $fields['billing']['billing_address_2'] );

	// Move contact details above the address block.
	$fields['billing']['billing_email']['priority'] = 21;
	$fields['billing']['billing_phone']['priority'] = 22;

	// Widen the remaining rows.
	$fields['billing']['billing_email']['class'] = array( 'form-row-wide' );

	return $fields;
}

Priority controls order within one group, not across the page. Reordering billing fields does not affect shipping. Core uses gaps of ten, so 21 and 22 place both fields between last name (20) and company (30) without moving anything else.

Reordering is low risk. Removing fields requires a business reason.

Tax and shipping fields

Do not remove country, state, or postcode from an address group. WooCommerce uses them to calculate tax and available shipping. Without them, customers can see the wrong total or no shipping method. If a field is inconvenient rather than unnecessary, make it optional instead of removing it.

Keep these fields even if they look expendable:

billing_country and billing_postcode because tax and shipping calculation depend on them
billing_phone when you ship physical goods and the carrier needs a contact number
billing_email because it is the dependable identifier for a guest order
Any field mapped by invoicing, accounting, or fulfilment software. Removing it can break exports long after checkout still looks healthy

How to Add a Custom Field to WooCommerce Checkout

For the classic WooCommerce checkout, render a custom field with woocommerce_form_field() on a checkout action hook. woocommerce_after_order_notes is a common location. woocommerce_before_order_notes, woocommerce_after_checkout_billing_form, and woocommerce_review_order_before_submit follow the same pattern. Prefix every field name to avoid collisions with WooCommerce or plugins.

Text and Textarea

add_action( 'woocommerce_after_order_notes', 'sm_text_checkout_fields' );

function sm_text_checkout_fields( $checkout ) {
	woocommerce_form_field(
		'sm_vat_number',
		array(
			'type'        => 'text',
			'label'       => __( 'VAT number', 'my-store' ),
			'placeholder' => 'DE123456789',
			'class'       => array( 'form-row-wide' ),
			'required'    => false,
		),
		$checkout->get_value( 'sm_vat_number' )
	);

	woocommerce_form_field(
		'sm_delivery_notes',
		array(
			'type'  => 'textarea',
			'label' => __( 'Delivery notes', 'my-store' ),
			'class' => array( 'form-row-wide' ),
		),
		$checkout->get_value( 'sm_delivery_notes' )
	);
}

$checkout->get_value() restores the input when validation returns the customer to the form. Without it, every failed submission clears what they entered.

Select and Radio

Both field types use an options array keyed by the value you intend to store:

woocommerce_form_field(
	'sm_delivery_window',
	array(
		'type'    => 'select',
		'label'   => __( 'Preferred delivery window', 'my-store' ),
		'class'   => array( 'form-row-wide' ),
		'options' => array(
			''        => __( 'No preference', 'my-store' ),
			'morning' => __( 'Morning, 8:00 to 12:00', 'my-store' ),
			'evening' => __( 'Evening, 16:00 to 20:00', 'my-store' ),
		),
	),
	$checkout->get_value( 'sm_delivery_window' )
);

Replace select with radio and WooCommerce renders the same options as radio inputs. Treat submitted values as untrusted. They are request strings, not proof that the customer selected a valid option. Compare each value with your own allowed list before saving it.

Checkbox

woocommerce_form_field(
	'sm_gift_wrap',
	array(
		'type'  => 'checkbox',
		'label' => __( 'Add gift wrapping', 'my-store' ),
		'class' => array( 'form-row-wide' ),
	),
	$checkout->get_value( 'sm_gift_wrap' )
);

An unchecked checkbox submits nothing. Test with isset() instead of comparing a value, then store an explicit yes or no. Otherwise you cannot distinguish a declined option from a field that never rendered.

WooCommerce Add File Upload to Checkout

File uploads are the exception. The classic checkout submits a serialized form over AJAX, and serialized forms do not include $_FILES. A plain type => file input can look correct while reaching the server empty.

Use two requests. Upload the file to your own endpoint when the customer selects it. Then place the returned attachment ID in a hidden field that the checkout submission can carry.

add_action( 'wp_ajax_sm_upload_checkout_file', 'sm_upload_checkout_file' );
add_action( 'wp_ajax_nopriv_sm_upload_checkout_file', 'sm_upload_checkout_file' );

function sm_upload_checkout_file() {
	check_ajax_referer( 'sm_checkout_upload', 'nonce' );

	if ( empty( $_FILES['sm_artwork']['name'] ) ) {
		wp_send_json_error( array( 'message' => 'No file received.' ), 400 );
	}

	if ( $_FILES['sm_artwork']['size'] > 2 * MB_IN_BYTES ) {
		wp_send_json_error( array( 'message' => 'Maximum file size is 2 MB.' ), 400 );
	}

	// Whitelist, not blacklist. No SVG, no archives, nothing executable.
	$allowed = array(
		'pdf'      => 'application/pdf',
		'png'      => 'image/png',
		'jpg|jpeg' => 'image/jpeg',
	);

	$checked = wp_check_filetype_and_ext(
		$_FILES['sm_artwork']['tmp_name'],
		sanitize_file_name( $_FILES['sm_artwork']['name'] ),
		$allowed
	);

	if ( empty( $checked['type'] ) ) {
		wp_send_json_error( array( 'message' => 'File type not allowed.' ), 400 );
	}

	require_once ABSPATH . 'wp-admin/includes/file.php';
	require_once ABSPATH . 'wp-admin/includes/media.php';
	require_once ABSPATH . 'wp-admin/includes/image.php';

	$attachment_id = media_handle_upload(
		'sm_artwork',
		0,
		array(),
		array(
			'test_form' => false,
			'mimes'     => $allowed,
		)
	);

	if ( is_wp_error( $attachment_id ) ) {
		wp_send_json_error( array( 'message' => $attachment_id->get_error_message() ), 400 );
	}

	wp_send_json_success( array( 'attachment_id' => (int) $attachment_id ) );
}

Your JavaScript sends the file and nonce to admin-ajax.php, then writes attachment_id to a hidden sm_artwork_id input. The save hook converts that ID to an integer and verifies that it references an acceptable attachment.

Public upload endpoint

This endpoint is available without a login, as it must be for stores that allow guest checkout. Treat it as a public upload form. Verify the actual file type with wp_check_filetype_and_ext(), not the filename extension. Limit size, reject SVG and archives, rate limit by IP, and clean up attachments that never reach an order. An unrestricted checkout upload is a serious site compromise risk.

Saving Custom Field Data to the Order

A rendered field without a save hook captures nothing. Checkout still completes, which is why this failure can stay invisible.

The Save Hook

Save through the order object on woocommerce_checkout_create_order. It runs before WooCommerce writes the order:

add_action( 'woocommerce_checkout_create_order', 'sm_save_custom_checkout_fields', 10, 2 );

function sm_save_custom_checkout_fields( $order, $data ) {
	// WooCommerce has already verified its own checkout nonce at this point.
	if ( ! empty( $_POST['sm_vat_number'] ) ) {
		$order->update_meta_data(
			'_sm_vat_number',
			sanitize_text_field( wp_unslash( $_POST['sm_vat_number'] ) )
		);
	}

	if ( ! empty( $_POST['sm_delivery_notes'] ) ) {
		$order->update_meta_data(
			'_sm_delivery_notes',
			sanitize_textarea_field( wp_unslash( $_POST['sm_delivery_notes'] ) )
		);
	}

	// Never trust a posted option value. Compare it against your own list.
	$window  = isset( $_POST['sm_delivery_window'] ) ? sanitize_key( wp_unslash( $_POST['sm_delivery_window'] ) ) : '';
	$allowed = array( 'morning', 'evening' );

	if ( in_array( $window, $allowed, true ) ) {
		$order->update_meta_data( '_sm_delivery_window', $window );
	}

	// An unchecked checkbox posts nothing, so write both states explicitly.
	$order->update_meta_data( '_sm_gift_wrap', isset( $_POST['sm_gift_wrap'] ) ? 'yes' : 'no' );
}

Do not call $order->save() here. WooCommerce saves the order immediately after this hook. Using the order object instead of update_post_meta() keeps the code compatible with HPOS order storage, where the posts table is no longer the authoritative order store.

If you inherit code on the older woocommerce_checkout_update_order_meta hook, you do not need to replace it immediately. You do need to use the CRUD layer:

add_action( 'woocommerce_checkout_update_order_meta', 'sm_legacy_save_custom_fields' );

function sm_legacy_save_custom_fields( $order_id ) {
	$order = wc_get_order( $order_id );

	if ( ! $order || empty( $_POST['sm_vat_number'] ) ) {
		return;
	}

	$order->update_meta_data( '_sm_vat_number', sanitize_text_field( wp_unslash( $_POST['sm_vat_number'] ) ) );
	$order->save();
}

Displaying It in the Admin Order Screen

Meta keys that begin with an underscore stay hidden in the generic custom-fields panel. Render them explicitly:

add_action( 'woocommerce_admin_order_data_after_billing_address', 'sm_show_custom_fields_in_admin' );

function sm_show_custom_fields_in_admin( $order ) {
	$vat    = $order->get_meta( '_sm_vat_number' );
	$window = $order->get_meta( '_sm_delivery_window' );

	if ( $vat ) {
		echo '<p><strong>' . esc_html__( 'VAT number', 'my-store' ) . ':</strong> ' . esc_html( $vat ) . '</p>';
	}

	if ( $window ) {
		echo '<p><strong>' . esc_html__( 'Delivery window', 'my-store' ) . ':</strong> ' . esc_html( $window ) . '</p>';
	}
}

Use $order->get_meta() rather than get_post_meta(), for the same HPOS compatibility reason as the save hook.

Including It in Order Emails

This filter appends your fields to the meta table in WooCommerce order emails:

add_filter( 'woocommerce_email_order_meta_fields', 'sm_email_order_meta_fields', 10, 3 );

function sm_email_order_meta_fields( $fields, $sent_to_admin, $order ) {
	$vat = $order->get_meta( '_sm_vat_number' );

	if ( $vat ) {
		$fields['sm_vat_number'] = array(
			'label' => __( 'VAT number', 'my-store' ),
			'value' => $vat,
		);
	}

	return $fields;
}

Check $sent_to_admin when a value belongs only in the internal email. This filter controls template output. It does not confirm that an email reached an inbox.

Validating WooCommerce Custom Checkout Fields

Validation is where a form change starts to affect completed orders.

Server Side Validation Hook

Use woocommerce_after_checkout_validation. It runs after core validation, gives you parsed $data and a WP_Error object, and lets you connect an error to one field:

add_action( 'woocommerce_after_checkout_validation', 'sm_validate_custom_checkout_fields', 10, 2 );

function sm_validate_custom_checkout_fields( $data, $errors ) {
	$vat = isset( $_POST['sm_vat_number'] ) ? sanitize_text_field( wp_unslash( $_POST['sm_vat_number'] ) ) : '';

	if ( '' === $vat ) {
		return;
	}

	// Normalize before judging: people paste spaces and dots.
	$vat = strtoupper( preg_replace( '/[^A-Za-z0-9]/', '', $vat ) );

	if ( ! preg_match( '/^[A-Z]{2}[A-Z0-9]{2,12}$/', $vat ) ) {
		$errors->add(
			'sm_vat_number',
			__( 'Enter your VAT number with the country prefix, for example DE123456789. Leave it empty if you do not have one.', 'my-store' )
		);
	}
}

The older woocommerce_checkout_process hook with wc_add_notice() still works. It cannot attach an error to a field, so the customer sees a page-level message without knowing which input needs attention.

Error Messages That Do Not Block Legitimate Orders

Overly strict validation is expensive because it rarely creates an error log or a support ticket. The customer sees a rejection they cannot resolve and leaves.

Silent validation failures

A rule that rejects valid customers can look like ordinary traffic in analytics. There is no PHP error and no failed payment. Orders from one country simply decline while an old regex remains unnoticed.

Before making a custom field required, check four things:

1Test every country you serve. Postcode and phone formats vary more than one pattern can cover.
2Normalize before rejecting. Remove spaces, dots, and hyphens, then uppercase values before comparison.
3Validate structure, not live lookups. A third-party outage must not become a checkout outage. Cache checks or verify after the order.
4Make the message actionable. Show the required format and say whether the field may stay empty.

Keep the field optional unless the order genuinely cannot be fulfilled without it.

Plugin Alternatives

Code gives you precise control. A plugin gives non-developers an admin interface. That trade-off matters more than many teams expect.

The official Checkout Field Editor extension provides a table for billing, shipping, and additional fields. You can add, remove, reorder, relabel, and change types such as select, radio, checkbox, and date. ThemeHigh's Checkout Field Editor offers similar controls, with a free tier and conditional logic in its paid version. Both store field definitions in the options table, outside version control. Those definitions also stop applying when the plugin is deactivated.

Code vs plugin decision

Situation	Better choice
One or two stable fields with one save path	Code
Non-technical staff change fields regularly	Field editor plugin
Conditional fields need changing without a deploy	Field editor plugin
Custom validation or an external lookup	Code
Field values must feed another system	Code

The plugin route wins when:

Nobody on the team can safely deploy PHP
The field set changes with campaigns or seasons
You need a date picker or conditional field without maintaining JavaScript
The alternative is a snippet in a parent theme that the next update will overwrite

What Breaks When You Add Custom Fields

Custom fields depend on filters and order storage. That makes them vulnerable to updates you did not write.

Validation Blocking Legitimate Orders

This failure has few visible symptoms. A required field or narrow pattern rejects real customers, often in countries you did not test. The site and payments remain healthy while orders from one segment stop arriving.

Fields Not Saving After a WooCommerce Update

Code written for legacy meta functions can stop reaching the order after a WooCommerce update, especially when order storage changes. The field still renders and checkout completes. The problem only appears when someone opens an order and finds the value missing.

Block Checkout Incompatibility

The Checkout block ignores woocommerce_checkout_fields and woocommerce_form_field(). Register custom fields with woocommerce_register_additional_checkout_field() on woocommerce_init in one of three locations: contact, address, or order. Moving to blocks without porting the fields removes them from the form.

Conflicts with Express Checkout

Apple Pay, Google Pay, and PayPal Express can build an order from wallet data and bypass the classic form. Your field may not render, its validation may not run, and no meta may be saved. Hide express buttons when a value is truly required, or collect the value after the order.

A checkout can look healthy while a field no longer saves. ShopMonitor runs the browser checkout and thank-you path on a schedule, so a failed path is visible in the next test run. It verifies the browser path only. It does not test inbox delivery or email receipt.

Adding the field is a one-time task. Keeping it reliable is ongoing work because the breaking change often arrives through an update elsewhere.

Use a repeatable checkout pass after every WooCommerce, theme, and plugin update. Submit every custom field and confirm that its value reached the order. Our guide to test the checkout covers the manual process. The wider set of changes you may make to customize the checkout page needs the same discipline.

Frequently asked questions

On the classic checkout, add woocommerce_form_field() to a checkout action such as woocommerce_after_order_notes. Give the field a prefixed name and pass $checkout->get_value() as the third argument so the value returns after a failed submission. For core fields, use woocommerce_checkout_fields because it controls labels, required state, and order. Rendering is only the first part. Without a save hook on woocommerce_checkout_create_order, WooCommerce discards the value when it creates the order.

Hook woocommerce_checkout_create_order, then call $order->update_meta_data( '_your_key', $sanitized_value ). Do not call $order->save(), because WooCommerce saves the order immediately after this hook. Avoid update_post_meta(), which writes to the posts table and is not reliable with high performance order storage. For older code on woocommerce_checkout_update_order_meta, load the order with wc_get_order(), update meta on the object, and call $order->save() yourself.

Yes, but not as a plain file input. The classic checkout sends a serialized AJAX form, which does not carry $_FILES. Upload the file in a separate request before submission, then store the resulting attachment ID in a hidden field. The endpoint is public on stores with guest checkout, so validate the actual file type with wp_check_filetype_and_ext() against a whitelist, cap file size, reject SVG and archives, and rate limit the endpoint.

The Checkout block does not use the classic form API. It ignores woocommerce_checkout_fields and woocommerce_form_field(), so shortcode-checkout snippets have no effect. Register the field with woocommerce_register_additional_checkout_field() on woocommerce_init and choose contact, address, or order. WooCommerce then renders, validates, saves, and displays it. Fields registered this way appear only in the block checkout.

Not always. Apple Pay, Google Pay, and PayPal Express can build the order from wallet data and bypass the classic form. Your field may not display, validation may not run, and meta may not be saved. If the value is essential to fulfilment, hide express buttons for the applicable products or conditions. For preferences such as a delivery window or gift wrapping, collect the value after the order and accept its absence.

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About the author

Written by the team at Winning Solutions, the agency behind ShopMonitor. We help WooCommerce teams build checkout fields that save reliably and validate without blocking legitimate orders.

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Group

Holds

Rendered when

billing

Billing name, address, phone and email

Always

shipping

Shipping name and address

The cart needs shipping and the customer uses another address

account

Username and password fields

Account creation at checkout is enabled

order

Order notes and, by convention, your own order-level fields

Always, unless you remove it

add_filter( 'woocommerce_checkout_fields', 'sm_checkout_fields' ); function sm_checkout_fields( $fields ) { $fields['billing']['billing_phone']['required'] = false; $fields['billing']['billing_phone']['label'] = 'Mobile number for delivery updates'; $fields['order']['order_comments']['placeholder'] = 'Anything the courier should know'; return $fields; }

add_filter( 'woocommerce_checkout_fields', 'sm_trim_checkout_fields' ); function sm_trim_checkout_fields( $fields ) { // Drop fields this store genuinely does not use. unset( $fields['billing']['billing_company'] ); unset( $fields['billing']['billing_address_2'] ); // Move contact details above the address block. $fields['billing']['billing_email']['priority'] = 21; $fields['billing']['billing_phone']['priority'] = 22; // Widen the remaining rows. $fields['billing']['billing_email']['class'] = array( 'form-row-wide' ); return $fields; }

add_action( 'woocommerce_after_order_notes', 'sm_text_checkout_fields' ); function sm_text_checkout_fields( $checkout ) { woocommerce_form_field( 'sm_vat_number', array( 'type' => 'text', 'label' => __( 'VAT number', 'my-store' ), 'placeholder' => 'DE123456789', 'class' => array( 'form-row-wide' ), 'required' => false, ), $checkout->get_value( 'sm_vat_number' ) ); woocommerce_form_field( 'sm_delivery_notes', array( 'type' => 'textarea', 'label' => __( 'Delivery notes', 'my-store' ), 'class' => array( 'form-row-wide' ), ), $checkout->get_value( 'sm_delivery_notes' ) ); }

woocommerce_form_field( 'sm_delivery_window', array( 'type' => 'select', 'label' => __( 'Preferred delivery window', 'my-store' ), 'class' => array( 'form-row-wide' ), 'options' => array( '' => __( 'No preference', 'my-store' ), 'morning' => __( 'Morning, 8:00 to 12:00', 'my-store' ), 'evening' => __( 'Evening, 16:00 to 20:00', 'my-store' ), ), ), $checkout->get_value( 'sm_delivery_window' ) );

woocommerce_form_field( 'sm_gift_wrap', array( 'type' => 'checkbox', 'label' => __( 'Add gift wrapping', 'my-store' ), 'class' => array( 'form-row-wide' ), ), $checkout->get_value( 'sm_gift_wrap' ) );

add_action( 'wp_ajax_sm_upload_checkout_file', 'sm_upload_checkout_file' ); add_action( 'wp_ajax_nopriv_sm_upload_checkout_file', 'sm_upload_checkout_file' ); function sm_upload_checkout_file() { check_ajax_referer( 'sm_checkout_upload', 'nonce' ); if ( empty( $_FILES['sm_artwork']['name'] ) ) { wp_send_json_error( array( 'message' => 'No file received.' ), 400 ); } if ( $_FILES['sm_artwork']['size'] > 2 * MB_IN_BYTES ) { wp_send_json_error( array( 'message' => 'Maximum file size is 2 MB.' ), 400 ); } // Whitelist, not blacklist. No SVG, no archives, nothing executable. $allowed = array( 'pdf' => 'application/pdf', 'png' => 'image/png', 'jpg|jpeg' => 'image/jpeg', ); $checked = wp_check_filetype_and_ext( $_FILES['sm_artwork']['tmp_name'], sanitize_file_name( $_FILES['sm_artwork']['name'] ), $allowed ); if ( empty( $checked['type'] ) ) { wp_send_json_error( array( 'message' => 'File type not allowed.' ), 400 ); } require_once ABSPATH . 'wp-admin/includes/file.php'; require_once ABSPATH . 'wp-admin/includes/media.php'; require_once ABSPATH . 'wp-admin/includes/image.php'; $attachment_id = media_handle_upload( 'sm_artwork', 0, array(), array( 'test_form' => false, 'mimes' => $allowed, ) ); if ( is_wp_error( $attachment_id ) ) { wp_send_json_error( array( 'message' => $attachment_id->get_error_message() ), 400 ); } wp_send_json_success( array( 'attachment_id' => (int) $attachment_id ) ); }

add_action( 'woocommerce_checkout_create_order', 'sm_save_custom_checkout_fields', 10, 2 ); function sm_save_custom_checkout_fields( $order, $data ) { // WooCommerce has already verified its own checkout nonce at this point. if ( ! empty( $_POST['sm_vat_number'] ) ) { $order->update_meta_data( '_sm_vat_number', sanitize_text_field( wp_unslash( $_POST['sm_vat_number'] ) ) ); } if ( ! empty( $_POST['sm_delivery_notes'] ) ) { $order->update_meta_data( '_sm_delivery_notes', sanitize_textarea_field( wp_unslash( $_POST['sm_delivery_notes'] ) ) ); } // Never trust a posted option value. Compare it against your own list. $window = isset( $_POST['sm_delivery_window'] ) ? sanitize_key( wp_unslash( $_POST['sm_delivery_window'] ) ) : ''; $allowed = array( 'morning', 'evening' ); if ( in_array( $window, $allowed, true ) ) { $order->update_meta_data( '_sm_delivery_window', $window ); } // An unchecked checkbox posts nothing, so write both states explicitly. $order->update_meta_data( '_sm_gift_wrap', isset( $_POST['sm_gift_wrap'] ) ? 'yes' : 'no' ); }

add_action( 'woocommerce_checkout_update_order_meta', 'sm_legacy_save_custom_fields' ); function sm_legacy_save_custom_fields( $order_id ) { $order = wc_get_order( $order_id ); if ( ! $order || empty( $_POST['sm_vat_number'] ) ) { return; } $order->update_meta_data( '_sm_vat_number', sanitize_text_field( wp_unslash( $_POST['sm_vat_number'] ) ) ); $order->save(); }

add_action( 'woocommerce_admin_order_data_after_billing_address', 'sm_show_custom_fields_in_admin' ); function sm_show_custom_fields_in_admin( $order ) { $vat = $order->get_meta( '_sm_vat_number' ); $window = $order->get_meta( '_sm_delivery_window' ); if ( $vat ) { echo '' . esc_html__( 'VAT number', 'my-store' ) . ': ' . esc_html( $vat ) . ''; } if ( $window ) { echo '' . esc_html__( 'Delivery window', 'my-store' ) . ': ' . esc_html( $window ) . ''; } }

add_filter( 'woocommerce_email_order_meta_fields', 'sm_email_order_meta_fields', 10, 3 ); function sm_email_order_meta_fields( $fields, $sent_to_admin, $order ) { $vat = $order->get_meta( '_sm_vat_number' ); if ( $vat ) { $fields['sm_vat_number'] = array( 'label' => __( 'VAT number', 'my-store' ), 'value' => $vat, ); } return $fields; }

add_action( 'woocommerce_after_checkout_validation', 'sm_validate_custom_checkout_fields', 10, 2 ); function sm_validate_custom_checkout_fields( $data, $errors ) { $vat = isset( $_POST['sm_vat_number'] ) ? sanitize_text_field( wp_unslash( $_POST['sm_vat_number'] ) ) : ''; if ( '' === $vat ) { return; } // Normalize before judging: people paste spaces and dots. $vat = strtoupper( preg_replace( '/[^A-Za-z0-9]/', '', $vat ) ); if ( ! preg_match( '/^[A-Z]{2}[A-Z0-9]{2,12}$/', $vat ) ) { $errors->add( 'sm_vat_number', __( 'Enter your VAT number with the country prefix, for example DE123456789. Leave it empty if you do not have one.', 'my-store' ) ); } }

Situation

Better choice

One or two stable fields with one save path

Code

Non-technical staff change fields regularly

Field editor plugin

Conditional fields need changing without a deploy

Field editor plugin

Custom validation or an external lookup

Code

Field values must feed another system

Code