diff --git a/tests/Feature/BucketUpdateTest.php b/tests/Feature/BucketUpdateTest.php
new file mode 100644
index 0000000..22da158
--- /dev/null
+++ b/tests/Feature/BucketUpdateTest.php
@@ -0,0 +1,169 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\Enums\BucketAllocationTypeEnum;
+use App\Enums\BucketTypeEnum;
+use App\Models\Bucket;
+use App\Models\Scenario;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class BucketUpdateTest extends TestCase
+{
+    use RefreshDatabase;
+
+    private Scenario $scenario;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        $this->scenario = Scenario::factory()->create();
+    }
+
+    public function test_can_update_starting_amount_only(): void
+    {
+        $bucket = Bucket::factory()->need()->fixedLimit(1000)->create([
+            'scenario_id' => $this->scenario->id,
+            'starting_amount' => 0,
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'starting_amount' => 500,
+        ]);
+
+        $response->assertOk();
+        $this->assertDatabaseHas('buckets', [
+            'id' => $bucket->id,
+            'starting_amount' => 500,
+            'name' => $bucket->name,
+            'type' => $bucket->type->value,
+        ]);
+    }
+
+    public function test_can_update_type_only(): void
+    {
+        $bucket = Bucket::factory()->need()->fixedLimit(1000)->create([
+            'scenario_id' => $this->scenario->id,
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'type' => 'want',
+        ]);
+
+        $response->assertOk();
+        $this->assertDatabaseHas('buckets', [
+            'id' => $bucket->id,
+            'type' => BucketTypeEnum::WANT->value,
+            'name' => $bucket->name,
+        ]);
+    }
+
+    public function test_can_update_buffer_multiplier_only(): void
+    {
+        $bucket = Bucket::factory()->need()->fixedLimit(1000)->create([
+            'scenario_id' => $this->scenario->id,
+            'buffer_multiplier' => 0,
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'buffer_multiplier' => 1.5,
+        ]);
+
+        $response->assertOk();
+        $this->assertDatabaseHas('buckets', [
+            'id' => $bucket->id,
+            'buffer_multiplier' => 1.5,
+        ]);
+    }
+
+    public function test_cannot_change_overflow_type(): void
+    {
+        $bucket = Bucket::factory()->overflow()->create([
+            'scenario_id' => $this->scenario->id,
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'type' => 'need',
+        ]);
+
+        $response->assertUnprocessable();
+        $response->assertJsonValidationErrors('type');
+    }
+
+    public function test_starting_amount_rejects_negative(): void
+    {
+        $bucket = Bucket::factory()->need()->fixedLimit(1000)->create([
+            'scenario_id' => $this->scenario->id,
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'starting_amount' => -100,
+        ]);
+
+        $response->assertUnprocessable();
+        $response->assertJsonValidationErrors('starting_amount');
+    }
+
+    public function test_buffer_multiplier_forced_to_zero_for_non_fixed_limit(): void
+    {
+        $bucket = Bucket::factory()->need()->fixedLimit(1000)->create([
+            'scenario_id' => $this->scenario->id,
+            'buffer_multiplier' => 1.5,
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'allocation_type' => 'percentage',
+            'allocation_value' => 25,
+        ]);
+
+        $response->assertOk();
+        $this->assertDatabaseHas('buckets', [
+            'id' => $bucket->id,
+            'allocation_type' => BucketAllocationTypeEnum::PERCENTAGE->value,
+            'buffer_multiplier' => 0,
+        ]);
+    }
+
+    public function test_response_includes_starting_amount(): void
+    {
+        $bucket = Bucket::factory()->need()->fixedLimit(1000)->create([
+            'scenario_id' => $this->scenario->id,
+            'starting_amount' => 500,
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'starting_amount' => 750,
+        ]);
+
+        $response->assertOk();
+        $response->assertJsonPath('bucket.starting_amount', 750);
+        $response->assertJsonPath('bucket.current_balance', 750);
+    }
+
+    public function test_can_update_name_only(): void
+    {
+        $bucket = Bucket::factory()->need()->fixedLimit(1000)->create([
+            'scenario_id' => $this->scenario->id,
+            'name' => 'Old Name',
+            'priority' => 1,
+        ]);
+
+        $response = $this->patchJson("/buckets/{$bucket->uuid}", [
+            'name' => 'New Name',
+        ]);
+
+        $response->assertOk();
+        $this->assertDatabaseHas('buckets', [
+            'id' => $bucket->id,
+            'name' => 'New Name',
+        ]);
+    }
+}