diff --git a/src/app/Console/Commands/AlgoliaSyncIndexSettings.php b/src/app/Console/Commands/AlgoliaSyncIndexSettings.php
new file mode 100644
index 00000000..821da2ff
--- /dev/null
+++ b/src/app/Console/Commands/AlgoliaSyncIndexSettings.php
@@ -0,0 +1,64 @@
+<?php
+
+namespace App\Console\Commands;
+
+use Algolia\AlgoliaSearch\Api\SearchClient;
+use App\Packages\Domains\WorldHeritage\Adapter\AlgoliaIndexSettingsSyncer;
+use Illuminate\Console\Command;
+
+class AlgoliaSyncIndexSettings extends Command
+{
+    protected $signature = 'algolia:sync-index-settings {--dry-run}';
+
+    protected $description = 'Apply the attributesForFaceting declared in code to the Algolia index settings.';
+
+    /**
+     * Every attribute the search Adapter filters or optional-filters on must
+     * be declared here, or Algolia rejects the request with a facet error.
+     * Attributes not used for filtering by the Adapter (e.g. country_names_jp,
+     * region, study_regions) are kept as plain facets rather than
+     * filterOnly() for now: whether the frontend needs their facet counts
+     * has not been confirmed (see Domains/README.md).
+     */
+    public const ATTRIBUTES_FOR_FACETING = [
+        'category',
+        'country',
+        'country_name_jp',
+        'country_names_jp',
+        'criteria',
+        'is_endangered',
+        'region',
+        'state_party_codes',
+        'study_region',
+        'study_regions',
+    ];
+
+    public function handle(): int
+    {
+        $indexName = config('algolia.algolia_index');
+
+        // Dry-run never talks to Algolia, so it must not depend on credentials being configured.
+        if ($this->option('dry-run')) {
+            $this->info('[dry-run] would set attributesForFaceting on index: ' . $indexName);
+            $this->line(json_encode(self::ATTRIBUTES_FOR_FACETING, JSON_PRETTY_PRINT));
+            return self::SUCCESS;
+        }
+
+        $appId = config('algolia.algolia_app_id');
+        $apiKey = config('algolia.algolia_write_api_key');
+
+        if (!$appId || !$apiKey || !$indexName) {
+            $this->error('Missing ALGOLIA_APP_ID / ALGOLIA_WRITE_API_KEY / ALGOLIA_INDEX');
+            return self::FAILURE;
+        }
+
+        // Resolved lazily (only reached once credentials are confirmed present) so
+        // dry-run and the missing-credentials path never touch the container binding.
+        $syncer = new AlgoliaIndexSettingsSyncer($this->laravel->make(SearchClient::class));
+        $syncer->syncAttributesForFaceting($indexName, self::ATTRIBUTES_FOR_FACETING);
+
+        $this->info("Done: attributesForFaceting synced on index={$indexName}");
+
+        return self::SUCCESS;
+    }
+}
diff --git a/src/app/Packages/Domains/README.md b/src/app/Packages/Domains/README.md
index 541f53cd..daf5047f 100644
--- a/src/app/Packages/Domains/README.md
+++ b/src/app/Packages/Domains/README.md
@@ -51,4 +51,18 @@ AlgoliaAdapter
 SearchResult (Ports)
     ↓
 Dto
-```
\ No newline at end of file
+```
+
+---
+
+## Algolia Index Settings
+
+`attributesForFaceting` is managed as code via `App\Console\Commands\AlgoliaSyncIndexSettings::ATTRIBUTES_FOR_FACETING`,
+applied with `php artisan algolia:sync-index-settings` (use `--dry-run` to preview without writing).
+Every attribute that `AlgoliaWorldHeritageSearchAdapter` filters or optional-filters on must be
+listed there, or Algolia rejects the request.
+
+All currently declared attributes are plain facets (facet counts enabled), none use `filterOnly()`.
+`country_names_jp`, `region`, and `study_regions` are not used as filters by the Adapter today, so
+they are candidates for `filterOnly()` to shrink the index — but this has not been changed yet,
+since whether the frontend relies on their facet counts has not been confirmed.
\ No newline at end of file
diff --git a/src/app/Packages/Domains/WorldHeritage/Adapter/AlgoliaIndexSettingsSyncer.php b/src/app/Packages/Domains/WorldHeritage/Adapter/AlgoliaIndexSettingsSyncer.php
new file mode 100644
index 00000000..0aabf350
--- /dev/null
+++ b/src/app/Packages/Domains/WorldHeritage/Adapter/AlgoliaIndexSettingsSyncer.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace App\Packages\Domains\WorldHeritage\Adapter;
+
+use Algolia\AlgoliaSearch\Api\SearchClient;
+
+class AlgoliaIndexSettingsSyncer
+{
+    public function __construct(
+        private SearchClient $client,
+    ) {}
+
+    public function syncAttributesForFaceting(string $indexName, array $attributesForFaceting): void
+    {
+        $res = $this->client->setSettings($indexName, [
+            'attributesForFaceting' => $attributesForFaceting,
+        ]);
+
+        $taskId = $res['taskID'] ?? null;
+        if ($taskId !== null) {
+            $this->client->waitForTask($indexName, $taskId);
+        }
+    }
+}
diff --git a/src/app/Packages/Domains/WorldHeritage/Tests/AlgoliaIndexSettingsSyncerTest.php b/src/app/Packages/Domains/WorldHeritage/Tests/AlgoliaIndexSettingsSyncerTest.php
new file mode 100644
index 00000000..b9ce2e47
--- /dev/null
+++ b/src/app/Packages/Domains/WorldHeritage/Tests/AlgoliaIndexSettingsSyncerTest.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace App\Packages\Domains\WorldHeritage\Tests;
+
+use Algolia\AlgoliaSearch\Api\SearchClient;
+use App\Packages\Domains\WorldHeritage\Adapter\AlgoliaIndexSettingsSyncer;
+use Mockery;
+use PHPUnit\Framework\Attributes\DoesNotPerformAssertions;
+use PHPUnit\Framework\TestCase;
+
+class AlgoliaIndexSettingsSyncerTest extends TestCase
+{
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        parent::tearDown();
+    }
+
+    #[DoesNotPerformAssertions]
+    public function test_waits_for_the_indexing_task_when_algolia_returns_a_task_id(): void
+    {
+        $client = Mockery::mock(SearchClient::class);
+        $client->shouldReceive('setSettings')
+            ->once()
+            ->with('world_heritages', ['attributesForFaceting' => ['category', 'country']])
+            ->andReturn(['taskID' => 42]);
+        $client->shouldReceive('waitForTask')->once()->with('world_heritages', 42);
+
+        $syncer = new AlgoliaIndexSettingsSyncer($client);
+        $syncer->syncAttributesForFaceting('world_heritages', ['category', 'country']);
+    }
+
+    #[DoesNotPerformAssertions]
+    public function test_does_not_wait_when_algolia_returns_no_task_id(): void
+    {
+        $client = Mockery::mock(SearchClient::class);
+        $client->shouldReceive('setSettings')->once()->andReturn([]);
+        $client->shouldNotReceive('waitForTask');
+
+        $syncer = new AlgoliaIndexSettingsSyncer($client);
+        $syncer->syncAttributesForFaceting('world_heritages', ['category']);
+    }
+}
diff --git a/src/app/Packages/Domains/WorldHeritage/Tests/AlgoliaSyncIndexSettingsTest.php b/src/app/Packages/Domains/WorldHeritage/Tests/AlgoliaSyncIndexSettingsTest.php
new file mode 100644
index 00000000..20c6a9c0
--- /dev/null
+++ b/src/app/Packages/Domains/WorldHeritage/Tests/AlgoliaSyncIndexSettingsTest.php
@@ -0,0 +1,83 @@
+<?php
+
+namespace App\Packages\Domains\WorldHeritage\Tests;
+
+use Algolia\AlgoliaSearch\Api\SearchClient;
+use App\Console\Commands\AlgoliaSyncIndexSettings;
+use Illuminate\Support\Facades\Artisan;
+use Mockery;
+use Tests\TestCase;
+
+class AlgoliaSyncIndexSettingsTest extends TestCase
+{
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        parent::tearDown();
+    }
+
+    public function test_dry_run_prints_attributes_for_faceting_without_calling_algolia(): void
+    {
+        $exitCode = Artisan::call('algolia:sync-index-settings', ['--dry-run' => true]);
+
+        $this->assertSame(0, $exitCode);
+
+        $output = Artisan::output();
+        foreach (AlgoliaSyncIndexSettings::ATTRIBUTES_FOR_FACETING as $attribute) {
+            $this->assertStringContainsString($attribute, $output);
+        }
+    }
+
+    public function test_fails_when_write_credentials_are_missing(): void
+    {
+        config(['algolia.algolia_write_api_key' => null]);
+
+        $exitCode = Artisan::call('algolia:sync-index-settings');
+
+        $this->assertSame(1, $exitCode);
+        $this->assertStringContainsString('Missing', Artisan::output());
+    }
+
+    public function test_syncs_attributes_for_faceting_when_credentials_are_present(): void
+    {
+        config([
+            'algolia.algolia_app_id' => 'dummy-app',
+            'algolia.algolia_write_api_key' => 'dummy-key',
+            'algolia.algolia_index' => 'world_heritages',
+        ]);
+
+        $client = Mockery::mock(SearchClient::class);
+        $client->shouldReceive('setSettings')
+            ->once()
+            ->with('world_heritages', ['attributesForFaceting' => AlgoliaSyncIndexSettings::ATTRIBUTES_FOR_FACETING])
+            ->andReturn(['taskID' => 123]);
+        $client->shouldReceive('waitForTask')->once()->with('world_heritages', 123);
+
+        $this->app->instance(SearchClient::class, $client);
+
+        $exitCode = Artisan::call('algolia:sync-index-settings');
+
+        $this->assertSame(0, $exitCode);
+        $this->assertStringContainsString('Done', Artisan::output());
+    }
+
+    public function test_attributes_for_faceting_covers_every_attribute_the_adapter_filters_on(): void
+    {
+        // Every attribute AlgoliaWorldHeritageSearchAdapter uses in $filters
+        // or $optionalFilters must be declared here, or Algolia rejects the
+        // facet filter request.
+        $usedByAdapter = [
+            'state_party_codes',
+            'country',
+            'country_name_jp',
+            'study_region',
+            'category',
+            'criteria',
+            'is_endangered',
+        ];
+
+        foreach ($usedByAdapter as $attribute) {
+            $this->assertContains($attribute, AlgoliaSyncIndexSettings::ATTRIBUTES_FOR_FACETING);
+        }
+    }
+}
diff --git a/src/app/Providers/AppServiceProvider.php b/src/app/Providers/AppServiceProvider.php
index a12b9fe0..369163c6 100644
--- a/src/app/Providers/AppServiceProvider.php
+++ b/src/app/Providers/AppServiceProvider.php
@@ -31,6 +31,13 @@ public function register(): void
 
             return new AlgoliaWorldHeritageSearchAdapter(client: $client, indexName: config('algolia.algolia_index'));
         });
+
+        // Write-key client for index administration (e.g. algolia:sync-index-settings).
+        // Resolved lazily via the container so callers only pay for it, and tests
+        // can swap it out, when they actually reach a code path that needs it.
+        $this->app->bind(SearchClient::class, function () {
+            return SearchClient::create(config('algolia.algolia_app_id'), config('algolia.algolia_write_api_key'));
+        });
     }
 
     /**