diff --git a/app/Models/Tracker.php b/app/Models/Tracker.php
index d37ed45..3fbdb2d 100644
--- a/app/Models/Tracker.php
+++ b/app/Models/Tracker.php
@@ -4,11 +4,16 @@
 
 namespace App\Models;
 
+use Database\Factories\TrackerFactory;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Database\Eloquent\Relations\BelongsTo;
 
 class Tracker extends Model
 {
+    /** @use HasFactory<TrackerFactory> */
+    use HasFactory;
+
     protected $fillable = [
         'user_id',
         'asset_id',
diff --git a/database/factories/TrackerFactory.php b/database/factories/TrackerFactory.php
new file mode 100644
index 0000000..4906e01
--- /dev/null
+++ b/database/factories/TrackerFactory.php
@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Database\Factories;
+
+use App\Models\Tracker;
+use App\Models\User;
+use Illuminate\Database\Eloquent\Factories\Factory;
+
+/**
+ * @extends Factory<Tracker>
+ */
+class TrackerFactory extends Factory
+{
+    protected $model = Tracker::class;
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function definition(): array
+    {
+        return [
+            'user_id' => fn () => User::default()->id,
+            'label' => 'Counter',
+            'unit' => 'units',
+            'count' => 0,
+        ];
+    }
+}
diff --git a/tests/Feature/CountBackfillMigrationTest.php b/tests/Feature/CountBackfillMigrationTest.php
new file mode 100644
index 0000000..d0d5ab5
--- /dev/null
+++ b/tests/Feature/CountBackfillMigrationTest.php
@@ -0,0 +1,153 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature;
+
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+use Tests\TestCase;
+
+class CountBackfillMigrationTest extends TestCase
+{
+    use RefreshDatabase;
+
+    private const MIGRATION = __DIR__.'/../../database/migrations/2026_08_15_000002_add_count_to_trackers_drop_entries.php';
+
+    // Each require returns a fresh anonymous-class instance; there is no name to collide.
+    private function migration(): object
+    {
+        return require self::MIGRATION;
+    }
+
+    /**
+     * Rebuild the pre-migration shape: entries present, trackers without a count.
+     */
+    private function revertToLedger(): void
+    {
+        $this->migration()->down();
+    }
+
+    private function makeTracker(): int
+    {
+        $userId = DB::table('users')->insertGetId([
+            'name' => 'Test',
+            'email' => 'ledger@example.test',
+            'password' => 'x',
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+
+        return DB::table('trackers')->insertGetId([
+            'user_id' => $userId,
+            'label' => 'Counter',
+            'unit' => 'units',
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+    }
+
+    private function addEntry(int $trackerId, string $quantity): void
+    {
+        DB::table('entries')->insert([
+            'tracker_id' => $trackerId,
+            'date' => now()->toDateString(),
+            'quantity' => $quantity,
+            'created_at' => now(),
+            'updated_at' => now(),
+        ]);
+    }
+
+    private function countFor(int $trackerId): int
+    {
+        return (int) DB::table('trackers')->where('id', $trackerId)->value('count');
+    }
+
+    public function test_backfill_sums_entries_into_count(): void
+    {
+        $this->revertToLedger();
+
+        $trackerId = $this->makeTracker();
+        $this->addEntry($trackerId, '10');
+        $this->addEntry($trackerId, '15');
+
+        $this->migration()->up();
+
+        $this->assertSame(25, $this->countFor($trackerId));
+    }
+
+    public function test_backfill_rounds_fractional_totals(): void
+    {
+        $this->revertToLedger();
+
+        $trackerId = $this->makeTracker();
+        $this->addEntry($trackerId, '1.4');
+        $this->addEntry($trackerId, '1.2');
+
+        $this->migration()->up();
+
+        $this->assertSame(3, $this->countFor($trackerId));
+    }
+
+    public function test_backfill_clamps_negative_totals_to_zero(): void
+    {
+        $this->revertToLedger();
+
+        $trackerId = $this->makeTracker();
+        $this->addEntry($trackerId, '5');
+        $this->addEntry($trackerId, '-9');
+
+        $this->migration()->up();
+
+        $this->assertSame(0, $this->countFor($trackerId));
+    }
+
+    public function test_tracker_without_entries_defaults_to_zero(): void
+    {
+        $this->revertToLedger();
+
+        $trackerId = $this->makeTracker();
+
+        $this->migration()->up();
+
+        $this->assertSame(0, $this->countFor($trackerId));
+    }
+
+    public function test_up_drops_the_entries_table(): void
+    {
+        $this->revertToLedger();
+        $this->assertTrue(Schema::hasTable('entries'));
+
+        $this->migration()->up();
+
+        $this->assertFalse(Schema::hasTable('entries'));
+        $this->assertTrue(Schema::hasColumn('trackers', 'count'));
+    }
+
+    // The two down() tests start from the migrated schema, so they do not call revertToLedger().
+    public function test_down_recreates_entries_from_count(): void
+    {
+        $trackerId = $this->makeTracker();
+        DB::table('trackers')->where('id', $trackerId)->update(['count' => 7]);
+
+        $this->migration()->down();
+
+        $this->assertTrue(Schema::hasTable('entries'));
+        $this->assertFalse(Schema::hasColumn('trackers', 'count'));
+
+        $entries = DB::table('entries')->where('tracker_id', $trackerId)->get();
+
+        $this->assertCount(1, $entries);
+        $this->assertSame(7.0, (float) $entries->first()->quantity);
+    }
+
+    public function test_down_writes_no_entry_for_a_zero_count(): void
+    {
+        $trackerId = $this->makeTracker();
+
+        $this->migration()->down();
+
+        $this->assertSame(0, DB::table('entries')->where('tracker_id', $trackerId)->count());
+    }
+}
diff --git a/tests/Feature/CounterTest.php b/tests/Feature/CounterTest.php
new file mode 100644
index 0000000..36037d4
--- /dev/null
+++ b/tests/Feature/CounterTest.php
@@ -0,0 +1,124 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature;
+
+use App\Models\Tracker;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Tests\TestCase;
+
+class CounterTest extends TestCase
+{
+    use RefreshDatabase;
+
+    private function tracker(int $count = 0): Tracker
+    {
+        return Tracker::factory()->create(['count' => $count]);
+    }
+
+    public function test_increment_adds_exactly_one(): void
+    {
+        $tracker = $this->tracker(5);
+
+        $response = $this->postJson('/increment');
+
+        $response->assertOk()->assertJson(['count' => 6]);
+        $this->assertSame(6, $tracker->refresh()->count);
+    }
+
+    public function test_increments_accumulate(): void
+    {
+        $tracker = $this->tracker();
+
+        $this->postJson('/increment');
+        $this->postJson('/increment');
+        $this->postJson('/increment');
+
+        $this->assertSame(3, $tracker->refresh()->count);
+    }
+
+    public function test_increment_returns_404_without_a_tracker(): void
+    {
+        $this->postJson('/increment')->assertNotFound();
+    }
+
+    public function test_count_can_be_set_to_an_absolute_value(): void
+    {
+        $tracker = $this->tracker(3);
+
+        $response = $this->patchJson('/count', ['count' => 250]);
+
+        $response->assertOk()->assertJson(['count' => 250]);
+        $this->assertSame(250, $tracker->refresh()->count);
+    }
+
+    public function test_count_can_be_set_to_zero(): void
+    {
+        $tracker = $this->tracker(42);
+
+        $this->patchJson('/count', ['count' => 0])->assertOk();
+
+        $this->assertSame(0, $tracker->refresh()->count);
+    }
+
+    /**
+     * @return array<string, array{mixed}>
+     */
+    public static function invalidCounts(): array
+    {
+        return [
+            'negative' => [-1],
+            'non-numeric string' => ['abc'],
+            'fractional' => [1.5],
+            'above unsigned int ceiling' => [4294967296],
+        ];
+    }
+
+    #[DataProvider('invalidCounts')]
+    public function test_count_rejects_invalid_values(mixed $value): void
+    {
+        $tracker = $this->tracker(7);
+
+        $this->patchJson('/count', ['count' => $value])
+            ->assertStatus(422)
+            ->assertJsonValidationErrors('count');
+
+        $this->assertSame(7, $tracker->refresh()->count);
+    }
+
+    public function test_count_requires_a_value(): void
+    {
+        $this->tracker();
+
+        $this->patchJson('/count', [])
+            ->assertStatus(422)
+            ->assertJsonValidationErrors('count');
+    }
+
+    public function test_count_returns_404_without_a_tracker(): void
+    {
+        $this->patchJson('/count', ['count' => 5])->assertNotFound();
+    }
+
+    public function test_counter_endpoints_return_json_not_redirects(): void
+    {
+        $this->tracker();
+
+        $this->postJson('/increment')
+            ->assertOk()
+            ->assertHeader('content-type', 'application/json');
+
+        $this->patchJson('/count', ['count' => 1])
+            ->assertOk()
+            ->assertHeader('content-type', 'application/json');
+    }
+
+    public function test_count_is_cast_to_an_integer(): void
+    {
+        $this->tracker(12);
+
+        $this->assertSame(12, Tracker::first()->count);
+    }
+}
diff --git a/tests/Feature/TrackerTest.php b/tests/Feature/TrackerTest.php
new file mode 100644
index 0000000..5a0673c
--- /dev/null
+++ b/tests/Feature/TrackerTest.php
@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature;
+
+use App\Models\Tracker;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Tests\TestCase;
+
+class TrackerTest extends TestCase
+{
+    use RefreshDatabase;
+
+    public function test_show_reports_no_tracker_on_a_fresh_install(): void
+    {
+        $this->getJson('/tracker')
+            ->assertOk()
+            ->assertJson(['exists' => false]);
+    }
+
+    public function test_show_returns_the_tracker_once_created(): void
+    {
+        Tracker::factory()->create(['count' => 9]);
+
+        $this->getJson('/tracker')
+            ->assertOk()
+            ->assertJson([
+                'exists' => true,
+                'tracker' => ['count' => 9],
+            ]);
+    }
+
+    public function test_a_tracker_can_be_created_without_a_label_or_unit(): void
+    {
+        $this->postJson('/tracker', [])->assertCreated();
+
+        $tracker = Tracker::first();
+
+        $this->assertSame('Counter', $tracker->label);
+        $this->assertSame('units', $tracker->unit);
+        $this->assertSame(0, $tracker->count);
+    }
+
+    public function test_a_new_counter_starts_at_zero(): void
+    {
+        $this->postJson('/tracker', []);
+
+        $this->getJson('/tracker')
+            ->assertOk()
+            ->assertJson(['tracker' => ['count' => 0]]);
+    }
+
+    public function test_creating_a_second_tracker_conflicts(): void
+    {
+        $this->postJson('/tracker', [])->assertCreated();
+        $this->postJson('/tracker', [])->assertStatus(409);
+
+        $this->assertSame(1, Tracker::count());
+    }
+}
diff --git a/tests/Unit/.gitkeep b/tests/Unit/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/tests/Unit/ExampleTest.php b/tests/Unit/ExampleTest.php
deleted file mode 100644
index 2cc6866..0000000
--- a/tests/Unit/ExampleTest.php
+++ /dev/null
@@ -1,16 +0,0 @@
-<?php
-
-namespace Tests\Unit;
-
-use Illuminate\Foundation\Testing\RefreshDatabase;
-use Tests\TestCase;
-
-class ExampleTest extends TestCase
-{
-    use RefreshDatabase;
-
-    public function test_that_true_is_true()
-    {
-        $this->assertTrue(true);
-    }
-}