diff --git a/tests/Feature/Api/PostApiTest.php b/tests/Feature/Api/PostApiTest.php
index 832ac9e1..27897358 100644
--- a/tests/Feature/Api/PostApiTest.php
+++ b/tests/Feature/Api/PostApiTest.php
@@ -297,6 +297,131 @@
         ->assertJsonValidationErrors(['label_ids.0']);
 });
 
+it('rejects creating a post with content_type not in the enum', function () {
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->postJson(route('api.posts.store'), [
+            'platforms' => [
+                ['social_account_id' => $this->socialAccount->id, 'content_type' => 'made_up_type'],
+            ],
+        ])
+        ->assertJsonValidationErrors(['platforms.0.content_type']);
+});
+
+it('rejects creating a post when content_type does not match the social account platform', function () {
+    // x_post on a LinkedIn account — ContentTypeMatchesPlatform should reject.
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->postJson(route('api.posts.store'), [
+            'platforms' => [
+                ['social_account_id' => $this->socialAccount->id, 'content_type' => 'x_post'],
+            ],
+        ])
+        ->assertJsonValidationErrors(['platforms.0.content_type']);
+});
+
+it('rejects creating a post with a label from another workspace', function () {
+    $otherWorkspace = Workspace::factory()->create();
+    $foreignLabel = WorkspaceLabel::factory()->create(['workspace_id' => $otherWorkspace->id]);
+
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->postJson(route('api.posts.store'), [
+            'platforms' => [
+                ['social_account_id' => $this->socialAccount->id, 'content_type' => 'linkedin_post'],
+            ],
+            'label_ids' => [$foreignLabel->id],
+        ])
+        ->assertJsonValidationErrors(['label_ids.0']);
+});
+
+it('rejects updating a post with a platforms[].id that belongs to another post', function () {
+    $myPost = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+    ]);
+
+    $otherPost = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+    ]);
+    $foreignPlatform = PostPlatform::factory()->linkedin()->create([
+        'post_id' => $otherPost->id,
+        'social_account_id' => $this->socialAccount->id,
+    ]);
+
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->putJson(route('api.posts.update', $myPost), [
+            'status' => 'draft',
+            'platforms' => [
+                ['id' => $foreignPlatform->id, 'content_type' => ContentType::LinkedInPost->value],
+            ],
+        ])
+        ->assertJsonValidationErrors(['platforms.0.id']);
+});
+
+it('rejects updating a post when content_type does not match the post_platform', function () {
+    $post = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+    ]);
+    $postPlatform = PostPlatform::factory()->linkedin()->create([
+        'post_id' => $post->id,
+        'social_account_id' => $this->socialAccount->id,
+        'enabled' => true,
+    ]);
+
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->putJson(route('api.posts.update', $post), [
+            'status' => 'draft',
+            'platforms' => [
+                ['id' => $postPlatform->id, 'content_type' => 'x_post'],
+            ],
+        ])
+        ->assertJsonValidationErrors(['platforms.0.content_type']);
+});
+
+it('rejects scheduled status without a future scheduled_at', function () {
+    $post = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+        'scheduled_at' => now()->subDay(),
+    ]);
+
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->putJson(route('api.posts.update', $post), [
+            'status' => 'scheduled',
+            'scheduled_at' => now()->subHour()->toIso8601String(),
+        ])
+        ->assertJsonValidationErrors(['scheduled_at']);
+});
+
+it('accepts draft status with no scheduled_at', function () {
+    $post = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+    ]);
+
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->putJson(route('api.posts.update', $post), [
+            'status' => 'draft',
+        ])
+        ->assertOk();
+});
+
+it('rejects creating a post with a past scheduled_at', function () {
+    $this->withHeaders(['Authorization' => 'Bearer '.$this->plainToken])
+        ->postJson(route('api.posts.store'), [
+            'platforms' => [
+                ['social_account_id' => $this->socialAccount->id, 'content_type' => 'linkedin_post'],
+            ],
+            'scheduled_at' => now()->subDay()->toIso8601String(),
+        ])
+        ->assertJsonValidationErrors(['scheduled_at']);
+});
+
 it('list posts returns correct structure', function () {
     Post::factory()->create([
         'workspace_id' => $this->workspace->id,
diff --git a/tests/Feature/Mcp/AttachMediaFromUrlToolTest.php b/tests/Feature/Mcp/AttachMediaFromUrlToolTest.php
index 76192ae1..ddfe710e 100644
--- a/tests/Feature/Mcp/AttachMediaFromUrlToolTest.php
+++ b/tests/Feature/Mcp/AttachMediaFromUrlToolTest.php
@@ -102,3 +102,37 @@
 
     $response->assertHasErrors(['Post not found.']);
 });
+
+test('rejects urls with non-http(s) schemes', function () {
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(AttachMediaFromUrlTool::class, [
+            'post_id' => $this->post->id,
+            'urls' => ['ftp://cdn.example.com/photo.jpg'],
+        ]);
+
+    $response->assertHasErrors();
+
+    expect($this->post->fresh()->media)->toBeEmpty();
+});
+
+test('rejects malformed url strings', function () {
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(AttachMediaFromUrlTool::class, [
+            'post_id' => $this->post->id,
+            'urls' => ['not-a-url-at-all'],
+        ]);
+
+    $response->assertHasErrors();
+});
+
+test('rejects more than 10 urls per call', function () {
+    $urls = collect(range(1, 11))->map(fn ($i) => "https://cdn.example.com/photo-{$i}.jpg")->all();
+
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(AttachMediaFromUrlTool::class, [
+            'post_id' => $this->post->id,
+            'urls' => $urls,
+        ]);
+
+    $response->assertHasErrors();
+});
diff --git a/tests/Feature/Mcp/PostPublishToolTest.php b/tests/Feature/Mcp/PostPublishToolTest.php
index a75fafb2..c3b29b90 100644
--- a/tests/Feature/Mcp/PostPublishToolTest.php
+++ b/tests/Feature/Mcp/PostPublishToolTest.php
@@ -119,6 +119,57 @@
     $response->assertHasErrors(['Cannot edit a published post.']);
 });
 
+test('update post rejects a platforms[].id that belongs to another post', function () {
+    $myPost = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+    ]);
+
+    $otherPost = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+    ]);
+    $foreignPlatform = PostPlatform::factory()->linkedin()->create([
+        'post_id' => $otherPost->id,
+        'social_account_id' => $this->socialAccount->id,
+    ]);
+
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(UpdatePostTool::class, [
+            'post_id' => $myPost->id,
+            'platforms' => [
+                ['id' => $foreignPlatform->id, 'content_type' => ContentType::LinkedInPost->value],
+            ],
+        ]);
+
+    $response->assertHasErrors();
+});
+
+test('update post rejects a content_type that does not match the post_platform', function () {
+    $post = Post::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'user_id' => $this->user->id,
+        'status' => PostStatus::Draft,
+    ]);
+    $postPlatform = PostPlatform::factory()->linkedin()->create([
+        'post_id' => $post->id,
+        'social_account_id' => $this->socialAccount->id,
+        'enabled' => true,
+    ]);
+
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(UpdatePostTool::class, [
+            'post_id' => $post->id,
+            'platforms' => [
+                ['id' => $postPlatform->id, 'content_type' => 'x_post'],
+            ],
+        ]);
+
+    $response->assertHasErrors();
+});
+
 // PublishPostTool
 
 test('publish post immediate dispatches PublishPost job', function () {
diff --git a/tests/Feature/Mcp/PostToolTest.php b/tests/Feature/Mcp/PostToolTest.php
index df7977d0..07bdb5f0 100644
--- a/tests/Feature/Mcp/PostToolTest.php
+++ b/tests/Feature/Mcp/PostToolTest.php
@@ -13,6 +13,7 @@
 use App\Models\SocialAccount;
 use App\Models\User;
 use App\Models\Workspace;
+use App\Models\WorkspaceLabel;
 use Illuminate\Testing\Fluent\AssertableJson;
 
 beforeEach(function () {
@@ -148,6 +149,61 @@
     $response->assertHasErrors();
 });
 
+test('create post rejects an inactive social account', function () {
+    $inactive = SocialAccount::factory()->create([
+        'workspace_id' => $this->workspace->id,
+        'platform' => Platform::LinkedIn,
+        'is_active' => false,
+    ]);
+
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(CreatePostTool::class, [
+            'platforms' => [
+                ['social_account_id' => $inactive->id, 'content_type' => 'linkedin_post'],
+            ],
+        ]);
+
+    $response->assertHasErrors();
+});
+
+test('create post rejects a content_type not in the enum', function () {
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(CreatePostTool::class, [
+            'platforms' => [
+                ['social_account_id' => $this->socialAccount->id, 'content_type' => 'made_up_type'],
+            ],
+        ]);
+
+    $response->assertHasErrors();
+});
+
+test('create post rejects a content_type that does not match the social account platform', function () {
+    // x_post on a LinkedIn account — ContentTypeMatchesPlatform should reject.
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(CreatePostTool::class, [
+            'platforms' => [
+                ['social_account_id' => $this->socialAccount->id, 'content_type' => 'x_post'],
+            ],
+        ]);
+
+    $response->assertHasErrors();
+});
+
+test('create post rejects a label_id from another workspace', function () {
+    $otherWorkspace = Workspace::factory()->create();
+    $foreignLabel = WorkspaceLabel::factory()->create(['workspace_id' => $otherWorkspace->id]);
+
+    $response = TryPostServer::actingAs($this->user)
+        ->tool(CreatePostTool::class, [
+            'platforms' => [
+                ['social_account_id' => $this->socialAccount->id, 'content_type' => 'linkedin_post'],
+            ],
+            'label_ids' => [$foreignLabel->id],
+        ]);
+
+    $response->assertHasErrors();
+});
+
 test('delete post removes from db', function () {
     $post = Post::factory()->create([
         'workspace_id' => $this->workspace->id,
diff --git a/tests/Unit/Rules/ContentTypeMatchesPlatformTest.php b/tests/Unit/Rules/ContentTypeMatchesPlatformTest.php
new file mode 100644
index 00000000..8a0fce74
--- /dev/null
+++ b/tests/Unit/Rules/ContentTypeMatchesPlatformTest.php
@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Enums\PostPlatform\ContentType;
+use App\Enums\SocialAccount\Platform;
+use App\Models\SocialAccount;
+use App\Models\Workspace;
+use App\Rules\ContentTypeMatchesPlatform;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+function runMatchesPlatformRule(string $contentType, ?string $accountId, array $extraData = []): array
+{
+    $errors = [];
+    $rule = (new ContentTypeMatchesPlatform)->setData(array_merge([
+        'platforms' => [
+            ['social_account_id' => $accountId, 'content_type' => $contentType],
+        ],
+    ], $extraData));
+
+    $rule->validate('platforms.0.content_type', $contentType, function (string $message) use (&$errors): void {
+        $errors[] = $message;
+    });
+
+    return $errors;
+}
+
+test('passes when content_type matches the social account platform', function () {
+    $workspace = Workspace::factory()->create();
+    $linkedin = SocialAccount::factory()->create([
+        'workspace_id' => $workspace->id,
+        'platform' => Platform::LinkedIn,
+    ]);
+
+    expect(runMatchesPlatformRule(ContentType::LinkedInPost->value, $linkedin->id))->toBe([]);
+    expect(runMatchesPlatformRule(ContentType::LinkedInCarousel->value, $linkedin->id))->toBe([]);
+});
+
+test('fails when content_type belongs to a different platform', function () {
+    $workspace = Workspace::factory()->create();
+    $linkedin = SocialAccount::factory()->create([
+        'workspace_id' => $workspace->id,
+        'platform' => Platform::LinkedIn,
+    ]);
+
+    $errors = runMatchesPlatformRule(ContentType::XPost->value, $linkedin->id);
+
+    expect($errors)->toHaveCount(1);
+    expect($errors[0])->toContain('not compatible');
+});
+
+test('passes when an instagram content_type is paired with an instagram-facebook account', function () {
+    $workspace = Workspace::factory()->create();
+    $igFacebook = SocialAccount::factory()->create([
+        'workspace_id' => $workspace->id,
+        'platform' => Platform::InstagramFacebook,
+    ]);
+
+    // instagram_feed lists Instagram as its primary platform but is also
+    // compatible with InstagramFacebook accounts via compatiblePlatforms().
+    expect(runMatchesPlatformRule(ContentType::InstagramFeed->value, $igFacebook->id))->toBe([]);
+    expect(runMatchesPlatformRule(ContentType::InstagramReel->value, $igFacebook->id))->toBe([]);
+});
+
+test('skips validation when social_account_id is missing', function () {
+    expect(runMatchesPlatformRule(ContentType::XPost->value, null))->toBe([]);
+});
+
+test('skips validation when content_type is not a known enum value', function () {
+    $workspace = Workspace::factory()->create();
+    $linkedin = SocialAccount::factory()->create([
+        'workspace_id' => $workspace->id,
+        'platform' => Platform::LinkedIn,
+    ]);
+
+    // Unknown content_types are caught by Rule::in elsewhere; this rule
+    // intentionally no-ops so it doesn't double-report.
+    expect(runMatchesPlatformRule('completely_made_up', $linkedin->id))->toBe([]);
+});
diff --git a/tests/Unit/Rules/ContentTypeMatchesPostPlatformTest.php b/tests/Unit/Rules/ContentTypeMatchesPostPlatformTest.php
new file mode 100644
index 00000000..cb4f22db
--- /dev/null
+++ b/tests/Unit/Rules/ContentTypeMatchesPostPlatformTest.php
@@ -0,0 +1,75 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Enums\PostPlatform\ContentType;
+use App\Enums\SocialAccount\Platform;
+use App\Models\Post;
+use App\Models\PostPlatform;
+use App\Models\SocialAccount;
+use App\Models\Workspace;
+use App\Rules\ContentTypeMatchesPostPlatform;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+uses(RefreshDatabase::class);
+
+function runMatchesPostPlatformRule(string $contentType, ?string $postPlatformId): array
+{
+    $errors = [];
+    $rule = (new ContentTypeMatchesPostPlatform)->setData([
+        'platforms' => [
+            ['id' => $postPlatformId, 'content_type' => $contentType],
+        ],
+    ]);
+
+    $rule->validate('platforms.0.content_type', $contentType, function (string $message) use (&$errors): void {
+        $errors[] = $message;
+    });
+
+    return $errors;
+}
+
+test('passes when content_type matches the post_platform social account', function () {
+    $workspace = Workspace::factory()->create();
+    $linkedin = SocialAccount::factory()->create([
+        'workspace_id' => $workspace->id,
+        'platform' => Platform::LinkedIn,
+    ]);
+    $post = Post::factory()->create(['workspace_id' => $workspace->id]);
+    $postPlatform = PostPlatform::factory()->linkedin()->create([
+        'post_id' => $post->id,
+        'social_account_id' => $linkedin->id,
+    ]);
+
+    expect(runMatchesPostPlatformRule(ContentType::LinkedInPost->value, $postPlatform->id))->toBe([]);
+    expect(runMatchesPostPlatformRule(ContentType::LinkedInCarousel->value, $postPlatform->id))->toBe([]);
+});
+
+test('fails when content_type belongs to a different platform than the post_platform', function () {
+    $workspace = Workspace::factory()->create();
+    $linkedin = SocialAccount::factory()->create([
+        'workspace_id' => $workspace->id,
+        'platform' => Platform::LinkedIn,
+    ]);
+    $post = Post::factory()->create(['workspace_id' => $workspace->id]);
+    $postPlatform = PostPlatform::factory()->linkedin()->create([
+        'post_id' => $post->id,
+        'social_account_id' => $linkedin->id,
+    ]);
+
+    $errors = runMatchesPostPlatformRule(ContentType::XPost->value, $postPlatform->id);
+
+    expect($errors)->toHaveCount(1);
+    expect($errors[0])->toContain('not compatible');
+});
+
+test('skips validation when platform id is missing', function () {
+    expect(runMatchesPostPlatformRule(ContentType::XPost->value, null))->toBe([]);
+});
+
+test('skips validation when post_platform does not exist', function () {
+    // Valid-format UUID that does not exist in the database. The rule
+    // intentionally no-ops so the missing-resource error is reported by
+    // the surrounding Rule::exists check rather than this rule.
+    expect(runMatchesPostPlatformRule(ContentType::XPost->value, '00000000-0000-0000-0000-000000000000'))->toBe([]);
+});