diff --git a/packages/Lvl0/FediDiscover/src/Actions/PollFediverseAction.php b/packages/Lvl0/FediDiscover/src/Actions/PollFediverseAction.php
index 3200b87..9d0f75c 100644
--- a/packages/Lvl0/FediDiscover/src/Actions/PollFediverseAction.php
+++ b/packages/Lvl0/FediDiscover/src/Actions/PollFediverseAction.php
@@ -4,18 +4,18 @@
 
 namespace Lvl0\FediDiscover\Actions;
 
-use Lvl0\FediDiscover\Clients\FediverseClient;
+use Lvl0\FediDiscover\Clients\FediverseClientInterface;
 use Lvl0\FediDiscover\Clients\FediversePost;
 use Lvl0\FediDiscover\Events\UrlDiscovered;
 use Lvl0\FediDiscover\Models\Instance;
 
 class PollFediverseAction
 {
-    public function __construct(private FediverseClient $client) {}
+    public function __construct(private FediverseClientInterface $client) {}
 
     public function execute(Instance $instance): void
     {
-        $posts = collect($this->client->fetchPostsSince($instance, $instance->last_seen_id));
+        $posts = $this->client->fetchPostsSince($instance, $instance->last_seen_id);
 
         $posts->each(function (FediversePost $post) use ($instance) {
             $this->processLinks($post, $instance);
diff --git a/packages/Lvl0/FediDiscover/src/Clients/FediverseClient.php b/packages/Lvl0/FediDiscover/src/Clients/FediverseClient.php
deleted file mode 100644
index c69049d..0000000
--- a/packages/Lvl0/FediDiscover/src/Clients/FediverseClient.php
+++ /dev/null
@@ -1,12 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Lvl0\FediDiscover\Clients;
-
-use Lvl0\FediDiscover\Models\Instance;
-
-interface FediverseClient
-{
-    public function fetchPostsSince(Instance $instance, ?string $lastSeenId): array;
-}
diff --git a/packages/Lvl0/FediDiscover/src/Clients/FediverseClientInterface.php b/packages/Lvl0/FediDiscover/src/Clients/FediverseClientInterface.php
new file mode 100644
index 0000000..f4a70a6
--- /dev/null
+++ b/packages/Lvl0/FediDiscover/src/Clients/FediverseClientInterface.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Lvl0\FediDiscover\Clients;
+
+use Illuminate\Support\Collection;
+use Lvl0\FediDiscover\Models\Instance;
+
+interface FediverseClientInterface
+{
+    /**
+     * Fetch posts newer than the given cursor.
+     *
+     * MUST return posts in newest-first order. Callers treat the
+     * first item as the new high-water mark.
+     *
+     * @return Collection<int, FediversePost>
+     */
+    public function fetchPostsSince(Instance $instance, ?string $lastSeenId): Collection;
+}
diff --git a/packages/Lvl0/FediDiscover/src/Clients/MastodonClient.php b/packages/Lvl0/FediDiscover/src/Clients/MastodonClient.php
new file mode 100644
index 0000000..eedea0e
--- /dev/null
+++ b/packages/Lvl0/FediDiscover/src/Clients/MastodonClient.php
@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Lvl0\FediDiscover\Clients;
+
+use Illuminate\Support\Collection;
+use Illuminate\Support\Facades\Http;
+use Lvl0\FediDiscover\Models\Instance;
+
+class MastodonClient implements FediverseClientInterface
+{
+    public function fetchPostsSince(Instance $instance, ?string $lastSeenId): Collection
+    {
+        $url = 'https://' . parse_url($instance->url, PHP_URL_HOST) . '/api/v1/timelines/public';
+
+        $params = $lastSeenId !== null ? ['min_id' => $lastSeenId] : [];
+
+        $response = Http::withHeaders([
+            'User-Agent' => config('fedi-discover.http.user_agent'),
+        ])->get($url, $params);
+
+        if (! $response->successful() || ! is_array($response->json())) {
+            return collect();
+        }
+
+        return collect($response->json())
+            ->map(fn (array $t) => new FediversePost(
+                cursorId: $t['id'],
+                selfUrl: $t['url'] ?? $t['uri'],
+                body: $t['content']
+            ));
+    }
+}
diff --git a/packages/Lvl0/FediDiscover/tests/Feature/MastodonClientTest.php b/packages/Lvl0/FediDiscover/tests/Feature/MastodonClientTest.php
new file mode 100644
index 0000000..d7a56bf
--- /dev/null
+++ b/packages/Lvl0/FediDiscover/tests/Feature/MastodonClientTest.php
@@ -0,0 +1,165 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Lvl0\FediDiscover\Tests\Feature;
+
+use Illuminate\Support\Collection;
+use Illuminate\Support\Facades\Http;
+use Lvl0\FediDiscover\Clients\FediversePost;
+use Lvl0\FediDiscover\Clients\MastodonClient;
+use Lvl0\FediDiscover\Config\InstanceType;
+use Lvl0\FediDiscover\Models\Instance;
+use Tests\TestCase;
+
+class MastodonClientTest extends TestCase
+{
+    public function test_it_hits_the_public_timeline_endpoint_of_the_instance(): void
+    {
+        Http::fake([
+            'mastodon.social/api/v1/timelines/public*' => Http::response([], 200),
+        ]);
+
+        (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        Http::assertSent(fn ($request) => str_starts_with($request->url(), 'https://mastodon.social/api/v1/timelines/public')
+            && $request->method() === 'GET'
+        );
+    }
+
+    public function test_it_omits_min_id_on_first_poll(): void
+    {
+        Http::fake(['*' => Http::response([], 200)]);
+
+        (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        Http::assertSent(fn ($request) => ! str_contains($request->url(), 'min_id'));
+    }
+
+    public function test_it_passes_min_id_on_subsequent_polls(): void
+    {
+        Http::fake(['*' => Http::response([], 200)]);
+
+        (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), '109876543210');
+
+        Http::assertSent(fn ($request) => str_contains($request->url(), 'min_id=109876543210'));
+    }
+
+    public function test_it_returns_an_empty_collection_when_the_api_returns_no_posts(): void
+    {
+        Http::fake(['*' => Http::response([], 200)]);
+
+        $posts = (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        $this->assertInstanceOf(Collection::class, $posts);
+        $this->assertTrue($posts->isEmpty());
+    }
+
+    public function test_it_maps_each_status_to_a_fediverse_post(): void
+    {
+        Http::fake([
+            '*' => Http::response([
+                $this->mastodonStatus(id: '109876543210', url: 'https://mastodon.social/@alice/109876543210', content: '<p>Hello</p>'),
+                $this->mastodonStatus(id: '109876543211', url: 'https://mastodon.social/@bob/109876543211', content: '<p>World</p>'),
+            ], 200),
+        ]);
+
+        $posts = (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        $this->assertCount(2, $posts);
+        $this->assertInstanceOf(FediversePost::class, $posts->first());
+        $this->assertSame('109876543210', $posts->first()->cursorId);
+        $this->assertSame('https://mastodon.social/@alice/109876543210', $posts->first()->selfUrl);
+        $this->assertSame('<p>Hello</p>', $posts->first()->body);
+    }
+
+    public function test_it_falls_back_to_uri_when_url_is_null(): void
+    {
+        Http::fake([
+            '*' => Http::response([
+                $this->mastodonStatus(
+                    id: '109876543210',
+                    url: null,
+                    uri: 'https://hachyderm.io/users/bob/statuses/5678',
+                    content: '<p>federated post</p>'
+                ),
+            ], 200),
+        ]);
+
+        $posts = (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        $this->assertSame('https://hachyderm.io/users/bob/statuses/5678', $posts->first()->selfUrl);
+    }
+
+    public function test_it_preserves_newest_first_ordering_from_the_api(): void
+    {
+        Http::fake([
+            '*' => Http::response([
+                $this->mastodonStatus(id: '300', url: 'https://mastodon.social/@a/300'),
+                $this->mastodonStatus(id: '200', url: 'https://mastodon.social/@b/200'),
+                $this->mastodonStatus(id: '100', url: 'https://mastodon.social/@c/100'),
+            ], 200),
+        ]);
+
+        $posts = (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        $this->assertSame(['300', '200', '100'], $posts->pluck('cursorId')->all());
+    }
+
+    public function test_it_returns_an_empty_collection_on_a_non_2xx_response(): void
+    {
+        Http::fake(['*' => Http::response('Too many requests', 429)]);
+
+        $posts = (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        $this->assertInstanceOf(Collection::class, $posts);
+        $this->assertTrue($posts->isEmpty());
+    }
+
+    public function test_it_returns_an_empty_collection_when_the_response_body_is_not_json(): void
+    {
+        Http::fake(['*' => Http::response('<html>error</html>', 200)]);
+
+        $posts = (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        $this->assertInstanceOf(Collection::class, $posts);
+        $this->assertTrue($posts->isEmpty());
+    }
+
+    public function test_it_sends_the_configured_user_agent(): void
+    {
+        Http::fake(['*' => Http::response([], 200)]);
+
+        (new MastodonClient)->fetchPostsSince($this->mastodonInstance(), null);
+
+        $expected = config('fedi-discover.http.user_agent');
+        Http::assertSent(fn ($request) => $request->header('User-Agent')[0] === $expected);
+    }
+
+    private function mastodonInstance(): Instance
+    {
+        return new Instance([
+            'type' => InstanceType::Mastodon,
+            'url' => 'https://mastodon.social',
+        ]);
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    private function mastodonStatus(
+        string $id,
+        ?string $url = null,
+        ?string $uri = null,
+        string $content = '<p>example</p>',
+    ): array {
+        return [
+            'id' => $id,
+            'url' => $url,
+            'uri' => $uri ?? "https://mastodon.social/users/x/statuses/{$id}",
+            'content' => $content,
+            'created_at' => '2026-04-25T10:00:00Z',
+            'account' => ['acct' => 'alice@mastodon.social'],
+        ];
+    }
+}
diff --git a/packages/Lvl0/FediDiscover/tests/Feature/PollFediverseActionTest.php b/packages/Lvl0/FediDiscover/tests/Feature/PollFediverseActionTest.php
index 48abc09..9d52f77 100644
--- a/packages/Lvl0/FediDiscover/tests/Feature/PollFediverseActionTest.php
+++ b/packages/Lvl0/FediDiscover/tests/Feature/PollFediverseActionTest.php
@@ -7,7 +7,7 @@
 use Illuminate\Foundation\Testing\RefreshDatabase;
 use Illuminate\Support\Facades\Event;
 use Lvl0\FediDiscover\Actions\PollFediverseAction;
-use Lvl0\FediDiscover\Clients\FediverseClient;
+use Lvl0\FediDiscover\Clients\FediverseClientInterface;
 use Lvl0\FediDiscover\Clients\FediversePost;
 use Lvl0\FediDiscover\Config\InstanceType;
 use Lvl0\FediDiscover\Events\UrlDiscovered;
@@ -171,11 +171,11 @@ public function test_it_passes_the_existing_last_seen_id_to_the_client(): void
     {
         $instance = $this->makeInstance(['last_seen_id' => '999']);
 
-        $client = Mockery::mock(FediverseClient::class);
+        $client = Mockery::mock(FediverseClientInterface::class);
         $client->shouldReceive('fetchPostsSince')
             ->once()
             ->with($instance, $instance->last_seen_id)
-            ->andReturn([]);
+            ->andReturn(collect());
 
         (new PollFediverseAction($client))->execute($instance);
     }
@@ -202,8 +202,8 @@ private function poll(array $posts, string $instanceUrl = 'https://mastodon.soci
      */
     private function pollInstance(Instance $instance, array $posts): void
     {
-        $client = Mockery::mock(FediverseClient::class);
-        $client->shouldReceive('fetchPostsSince')->andReturn($posts);
+        $client = Mockery::mock(FediverseClientInterface::class);
+        $client->shouldReceive('fetchPostsSince')->andReturn(collect($posts));
 
         (new PollFediverseAction($client))->execute($instance);
     }
diff --git a/phpunit.xml b/phpunit.xml
index 46d97dd..9ca208c 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -3,6 +3,11 @@
          xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
          bootstrap="vendor/autoload.php"
          colors="true"
+    processIsolation="false"
+    displayDetailsOnPhpunitDeprecations="true"
+    displayDetailsOnTestsThatTriggerErrors="true"
+    displayDetailsOnTestsThatTriggerWarnings="true"
+    displayDetailsOnTestsThatTriggerNotices="true"
 >
     <testsuites>
         <testsuite name="Unit">
@@ -36,5 +41,7 @@
         <env name="PULSE_ENABLED" value="false"/>
         <env name="TELESCOPE_ENABLED" value="false"/>
         <env name="NIGHTWATCH_ENABLED" value="false"/>
+        <ini name="display_errors" value="On"/>
+        <ini name="error_reporting" value="-1"/>
     </php>
 </phpunit>