diff --git a/includes/class-tmdo-hivepress-entity-groups.php b/includes/class-tmdo-hivepress-entity-groups.php
index 27d41ee..184c367 100644
--- a/includes/class-tmdo-hivepress-entity-groups.php
+++ b/includes/class-tmdo-hivepress-entity-groups.php
@@ -76,6 +76,7 @@ final class TMDO_HivePress_Entity_Groups {
 		self::register_hp_request_core_group();
 		self::register_hp_vendor_core_group();
 		self::register_hp_user_group();
+		self::register_hp_listing_attributes_group();
 	}
 
 	// ── Group definitions ────────────────────────────────────────────────────
@@ -271,6 +272,39 @@ final class TMDO_HivePress_Entity_Groups {
 			)
 		);
 	}
+	/**
+	 * A site's own HivePress listing attributes (created under Listings →
+	 * Attributes, e.g. a "Warranty" number → hp_warranty), opt-in through the
+	 * `tmdo_hp_listing_attribute_fields` filter: `array( 'hp_warranty' => 'integer' )`.
+	 *
+	 * They get a group of their own — a new table, each column indexed at
+	 * creation — so hp_listing_core and its pinned definition stay unchanged.
+	 * Keys another group already manages, keys without the hp_ prefix and
+	 * unknown types are ignored. Backfill with `wp tmdo post-migrate-group`.
+	 *
+	 * @return void
+	 */
+	private static function register_hp_listing_attributes_group(): void {
+		$fields = array();
+		foreach ( (array) apply_filters( 'tmdo_hp_listing_attribute_fields', array() ) as $key => $type ) {
+			$key = (string) $key;
+			if ( 1 !== preg_match( '/^hp_[a-z0-9_]+$/', $key )
+				|| ! in_array( $type, TMDO_Entity_Registry::VALID_TYPES, true )
+				|| null !== TMDO_Entity_Registry::get_field( 'post', $key, 'hp_listing' ) ) {
+				continue;
+			}
+			$fields[] = array(
+				'key'        => $key,
+				'type'       => $type,
+				'searchable' => true,
+				'label'      => 'Site listing attribute',
+			);
+		}
+		if ( $fields ) {
+			TMDO_Entity_Registry::register_group( 'post', 'hp_listing_attrs', $fields, array( 'post_types' => array( 'hp_listing' ) ) );
+		}
+	}
+
 	/**
 	 * HivePress request core meta keys (post_type=hp_request).
 	 *
diff --git a/tests/unit/HivePressEntityGroupsTest.php b/tests/unit/HivePressEntityGroupsTest.php
index 6eea5f1..44c170f 100644
--- a/tests/unit/HivePressEntityGroupsTest.php
+++ b/tests/unit/HivePressEntityGroupsTest.php
@@ -73,6 +73,39 @@ class HivePressEntityGroupsTest extends TestCase {
 		);
 	}
 
+	public function test_site_listing_attributes_are_opt_in(): void {
+		$this->assertSame( array(), TMDO_Entity_Registry::get_group_fields( 'post', 'hp_listing_attrs' ) );
+	}
+
+	/**
+	 * A site flattens its own HivePress listing attributes (e.g. a "Warranty"
+	 * number attribute → hp_warranty) in a group of their own: a new table,
+	 * indexed at creation; hp_listing_core and its pinned hash stay as they are.
+	 */
+	public function test_site_listing_attributes_get_their_own_indexed_group(): void {
+		$fields = static fn() => array(
+			'hp_warranty' => 'integer',
+			'hp_price'    => 'decimal', // Already in hp_listing_core.
+			'warranty'    => 'integer', // Not a HivePress key.
+			'hp_color'    => 'colour', // Unknown type.
+		);
+		add_filter( 'tmdo_hp_listing_attribute_fields', $fields );
+		try {
+			TMDO_Entity_Registry::init();
+			TMDO_Entity_Registry::register_adapter( 'post', $this->createMock( TMDO_Entity_Adapter_Interface::class ) );
+			TMDO_Entity_Registry::register_adapter( 'user', $this->createMock( TMDO_Entity_Adapter_Interface::class ) );
+			TMDO_HivePress_Entity_Groups::register_entity_fields();
+		} finally {
+			$GLOBALS['_wp_filter_callbacks']['tmdo_hp_listing_attribute_fields'] = array();
+		}
+
+		$this->assertSame( array( 'hp_warranty' ), TMDO_Entity_Registry::get_group_keys( 'post', 'hp_listing_attrs' ) );
+		$this->assertTrue( (bool) TMDO_Entity_Registry::get_group_fields( 'post', 'hp_listing_attrs' )[0]['searchable'] );
+		$this->assertSame( array( 'hp_listing' ), TMDO_Entity_Registry::get_group_post_types( 'post', 'hp_listing_attrs' ) );
+		$this->assertSame( 'hp_listing_core', TMDO_Entity_Registry::get_field( 'post', 'hp_price' )['group'] );
+		$this->test_definitions_match_persisted_schema_hashes();
+	}
+
 	public function test_shared_keys_keep_their_current_owner(): void {
 		foreach ( self::SHARED_KEY_OWNERS as $key => $group ) {
 			$this->assertSame( $group, TMDO_Entity_Registry::get_field( 'post', $key )['group'], $key );