diff --git a/src/Integrations/Divi/DiviIntegration.php b/src/Integrations/Divi/DiviIntegration.php
index 2eca391..75a8134 100644
--- a/src/Integrations/Divi/DiviIntegration.php
+++ b/src/Integrations/Divi/DiviIntegration.php
@@ -15,6 +15,7 @@ use LIT\MCP\Integrations\Divi\Library\GlobalEdits;
 use LIT\MCP\Integrations\Divi\Library\GlobalUsages;
 use LIT\MCP\Integrations\Divi\Library\LibraryAccess;
 use LIT\MCP\Integrations\Divi\Library\LibraryIntegration;
+use LIT\MCP\Integrations\Divi\Library\SimilarSections;
 use LIT\MCP\Integrations\Divi\Pages\DiviComposition;
 use LIT\MCP\Integrations\Divi\Pages\DiviContentComposer;
 use LIT\MCP\Integrations\Divi\Pages\DiviDeleteAbility;
@@ -194,7 +195,8 @@ final class DiviIntegration implements Integration
             $this->design,
             new DiviComposition($this->modules, $this->design),
             new GlobalEdits($this->access, new GlobalUsages(null, $this->access->roles())),
-            new ThemeBuilderEdits($this->themeBuilderAccess, fields: new DynamicFields($this->schema))
+            new ThemeBuilderEdits($this->themeBuilderAccess, fields: new DynamicFields($this->schema)),
+            new SimilarSections($this->access)
         );
     }
 
diff --git a/src/Integrations/Divi/Library/SimilarSections.php b/src/Integrations/Divi/Library/SimilarSections.php
new file mode 100644
index 0000000..2fe2feb
--- /dev/null
+++ b/src/Integrations/Divi/Library/SimilarSections.php
@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Integrations\Divi\Library;
+
+use LIT\MCP\Integrations\Divi\BlockTree\Block;
+use LIT\MCP\Integrations\Divi\BlockTree\Fingerprint;
+use LIT\MCP\Integrations\Divi\BlockTree\LibraryContent;
+use LIT\MCP\Integrations\Divi\BlockTree\MalformedMarkup;
+use LIT\MCP\Integrations\Divi\BlockTree\Parser;
+use LIT\MCP\Integrations\Divi\Pages\DiviChange;
+
+defined('ABSPATH') || exit;
+
+/**
+ * The quality warning "similar section" (spec §5.5, D6, E11): an inserted section built like a section entry of
+ * the Divi Library (Fingerprint::structure) – compared with library entries only (small; at most MAX_ITEMS, the
+ * ones the user may edit), read only when a write inserts a section and then once per request (kept in memory; no
+ * index or meta, F31). Global instances are already linked to the library and never warn. Only while library IDs
+ * may be named (ruling P13). The warning names the entry's title and ID, never the page's texts. Not final so the
+ * writer can be tested with a mock.
+ */
+class SimilarSections
+{
+    public const MAX_ITEMS = 200;
+
+    /** @var array<string, array{id: int, title: string}>|null Structure fingerprint => entry. */
+    private ?array $index = null;
+
+    public function __construct(private LibraryAccess $access, private Parser $parser = new Parser())
+    {
+    }
+
+    /** @return list<string> */
+    public function warnings(DiviChange $change): array
+    {
+        if (! $this->access->revealsIds()) {
+            return [];
+        }
+
+        $warnings = [];
+        foreach ($change->entries() as $entry) {
+            $block = $entry['block'];
+            if (
+                $entry['action'] !== 'inserted'
+                || ! $block instanceof Block
+                || $block->name() !== 'divi/section'
+                || $block->isOpaque()
+                || $block->isGlobal()
+            ) {
+                continue;
+            }
+            $match = $this->index()[Fingerprint::structure($block)] ?? null;
+            if ($match !== null) {
+                $warnings[] = sprintf(
+                    'Ein gleich aufgebauter Abschnitt liegt in der Divi-Bibliothek: „%s“ (%d) – lit-library-insert '
+                        . 'erwägen; weitere Vorkommen mit lit/library-find-similar.',
+                    $match['title'],
+                    $match['id']
+                );
+            }
+        }
+
+        return array_values(array_unique($warnings));
+    }
+
+    /** @return array<string, array{id: int, title: string}> */
+    private function index(): array
+    {
+        if ($this->index !== null) {
+            return $this->index;
+        }
+
+        $this->index = [];
+        foreach ($this->access->store()->find(['layout_type' => 'section'], self::MAX_ITEMS - 1, 0) as $item) {
+            if (! current_user_can('edit_post', (int) $item->ID)) {
+                continue;
+            }
+            try {
+                $roots = LibraryContent::roots(LibraryContent::load($this->parser, (string) $item->post_content));
+            } catch (MalformedMarkup) {
+                continue;
+            }
+            if (count($roots) === 1 && $roots[0]->name() === 'divi/section') {
+                $this->index[Fingerprint::structure($roots[0])] ??= [
+                    'id' => (int) $item->ID,
+                    'title' => (string) $item->post_title,
+                ];
+            }
+        }
+
+        return $this->index;
+    }
+}
diff --git a/src/Integrations/Divi/Pages/DiviWriter.php b/src/Integrations/Divi/Pages/DiviWriter.php
index 470678c..c3ca304 100644
--- a/src/Integrations/Divi/Pages/DiviWriter.php
+++ b/src/Integrations/Divi/Pages/DiviWriter.php
@@ -14,6 +14,7 @@ use LIT\MCP\Integrations\Divi\BlockTree\Outline;
 use LIT\MCP\Integrations\Divi\BlockTree\Serializer;
 use LIT\MCP\Integrations\Divi\Design\DesignSystemReader;
 use LIT\MCP\Integrations\Divi\Library\GlobalEdits;
+use LIT\MCP\Integrations\Divi\Library\SimilarSections;
 use LIT\MCP\Integrations\Divi\ThemeBuilder\ThemeBuilderEdits;
 use LIT\MCP\Integrations\WordPress\PostSaveFollowUp;
 use WP_Error;
@@ -27,13 +28,17 @@ defined('ABSPATH') || exit;
  * then lit_mcp_after_save, change log and the ToolResult with changed nodes, affected outline,
  * quality warnings (spec §5.5), revision_id, the new rev and tree_rev. commit() is the entry point
  * of the tools: library entries additionally pass GlobalEdits (shape, dry run/confirm, backup), Theme
- * Builder layouts ThemeBuilderEdits (live layouts: dry run/confirm, backup; ruling Q2/Q9).
+ * Builder layouts ThemeBuilderEdits (live layouts: dry run/confirm, backup; ruling Q2/Q9). SimilarSections adds
+ * the "similar section" warning (spec §5.5, E11) – not for lit/library-insert, whose sections come from the library.
  */
 final class DiviWriter
 {
     public const OUTLINE_TRUNCATED = 'Die Übersicht der geänderten Abschnitte ist gekürzt; vollständig mit '
         . 'lit-divi-outline lesen.';
 
+    /** Inserts library entries: no advice to use the library (SimilarSections). */
+    private const FROM_LIBRARY = 'lit/library-insert';
+
     public function __construct(
         private DiviPageLoader $loader,
         private DiviSaver $saver,
@@ -41,7 +46,8 @@ final class DiviWriter
         private DesignSystemReader $design,
         private DiviComposition $composition,
         private ?GlobalEdits $globals = null,
-        private ?ThemeBuilderEdits $themeBuilder = null
+        private ?ThemeBuilderEdits $themeBuilder = null,
+        private ?SimilarSections $similar = null
     ) {
     }
 
@@ -106,7 +112,8 @@ final class DiviWriter
 
         $index = NodeIndex::build($page->document);
         $quality = $this->composition->warnings()->collect($index, $change->touched());
-        $warnings = array_merge($change->warnings(), $quality);
+        $similar = $ability === self::FROM_LIBRARY ? [] : ($this->similar?->warnings($change) ?? []);
+        $warnings = array_merge($change->warnings(), $quality, $similar);
 
         try {
             $saved = $this->saver->save($post, $content, $scope);
diff --git a/tests/Support/DiviWriterFixture.php b/tests/Support/DiviWriterFixture.php
index a9e1a87..8a54352 100644
--- a/tests/Support/DiviWriterFixture.php
+++ b/tests/Support/DiviWriterFixture.php
@@ -6,6 +6,7 @@ namespace LIT\MCP\Tests\Support;
 
 use LIT\MCP\Integrations\Divi\Design\DesignSystemReader;
 use LIT\MCP\Integrations\Divi\Library\GlobalEdits;
+use LIT\MCP\Integrations\Divi\Library\SimilarSections;
 use LIT\MCP\Integrations\Divi\Pages\DiviComposition;
 use LIT\MCP\Integrations\Divi\Pages\DiviPageLoader;
 use LIT\MCP\Integrations\Divi\Pages\DiviSaver;
@@ -102,7 +103,8 @@ final class DiviWriterFixture
         bool $unfiltered = false,
         ?DiviPageLoader $loader = null,
         ?GlobalEdits $globals = null,
-        ?ThemeBuilderEdits $themeBuilder = null
+        ?ThemeBuilderEdits $themeBuilder = null,
+        ?SimilarSections $similar = null
     ): DiviWriter {
         $design = self::designReader();
 
@@ -113,7 +115,8 @@ final class DiviWriterFixture
             $design,
             self::composition($design, $unfiltered),
             $globals,
-            $themeBuilder
+            $themeBuilder,
+            $similar
         );
     }
 }
diff --git a/tests/Unit/Integrations/Divi/Library/SimilarSectionsTest.php b/tests/Unit/Integrations/Divi/Library/SimilarSectionsTest.php
new file mode 100644
index 0000000..ee8c9ca
--- /dev/null
+++ b/tests/Unit/Integrations/Divi/Library/SimilarSectionsTest.php
@@ -0,0 +1,101 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Tests\Unit\Integrations\Divi\Library;
+
+use LIT\MCP\Integrations\Divi\BlockTree\Block;
+use LIT\MCP\Integrations\Divi\BlockTree\LibraryContent;
+use LIT\MCP\Integrations\Divi\BlockTree\Parser;
+use LIT\MCP\Integrations\Divi\Library\SimilarSections;
+use LIT\MCP\Integrations\Divi\Pages\DiviChange;
+use LIT\MCP\Tests\Support\DiviFixtures;
+use LIT\MCP\Tests\Support\LibraryFixtures;
+use LIT\MCP\Tests\Unit\TestCase;
+
+final class SimilarSectionsTest extends TestCase
+{
+    private static function sectionLike1055(): Block
+    {
+        $root = LibraryContent::roots(LibraryContent::load(
+            new Parser(),
+            DiviFixtures::markup('stage3/library--library-abschnitt.html')
+        ))[0]->copy();
+        $blurb = $root->children()[0]->children()[0]->children()[0];
+        $attrs = $blurb->attrs();
+        $attrs['title']['innerContent']['desktop']['value'] = 'Neuer Titel';
+        $blurb->setAttrs($attrs);
+
+        return $root;
+    }
+
+    /** @param list<string> $deniedRoles */
+    private static function similar(array $deniedRoles = []): SimilarSections
+    {
+        LibraryFixtures::given([LibraryFixtures::item(1055), LibraryFixtures::item(1058)]);
+        $store = LibraryFixtures::store();
+        $store->allows('find')->andReturn([LibraryFixtures::item(1055), LibraryFixtures::item(1058)]);
+
+        return new SimilarSections(LibraryFixtures::access($deniedRoles, true, $store));
+    }
+
+    public function testWarnsForAnInsertedSectionBuiltLikeALibrarySection(): void
+    {
+        $change = (new DiviChange('1 Divi-Knoten eingefügt'))->record(self::sectionLike1055(), 'inserted');
+
+        $warnings = self::similar()->warnings($change);
+
+        self::assertCount(1, $warnings);
+        self::assertStringContainsString('„[Fixture] 1055“ (1055)', $warnings[0]);
+        self::assertStringContainsString('lit-library-insert', $warnings[0]);
+        self::assertStringContainsString('lit/library-find-similar', $warnings[0]);
+    }
+
+    public function testOnlyInsertedSectionsAndOnlyWithLibraryAccess(): void
+    {
+        $moved = (new DiviChange('verschoben'))->record(self::sectionLike1055(), 'moved');
+        $inserted = (new DiviChange('eingefügt'))->record(self::sectionLike1055(), 'inserted');
+
+        self::assertSame([], self::similar()->warnings($moved));
+        self::assertSame([], self::similar(['divi_library'])->warnings($inserted));
+    }
+
+    /** The library is read once per request, at most MAX_ITEMS section entries, only those the user may edit. */
+    public function testReadsTheLibraryOnceBoundedAndOnlyEditableEntries(): void
+    {
+        LibraryFixtures::given([LibraryFixtures::item(1055)]);
+        \Brain\Monkey\Functions\when('current_user_can')->alias(
+            static fn (string $cap, mixed ...$args): bool => ! ($cap === 'edit_post' && ($args[0] ?? 0) === 1055)
+        );
+        $store = LibraryFixtures::store();
+        $store->expects('find')->once()->with(['layout_type' => 'section'], SimilarSections::MAX_ITEMS - 1, 0)
+            ->andReturn([LibraryFixtures::item(1055)]);
+        $similar = new SimilarSections(LibraryFixtures::access([], true, $store));
+        $change = (new DiviChange('eingefügt'))->record(self::sectionLike1055(), 'inserted');
+
+        self::assertSame([], $similar->warnings($change), 'entry 1055 is not editable');
+        self::assertSame([], $similar->warnings($change));
+    }
+
+    /** No section inserted: the library is not read at all (cheap on every write). */
+    public function testWithoutAnInsertedSectionTheLibraryIsNotRead(): void
+    {
+        LibraryFixtures::given([]);
+        $store = LibraryFixtures::store();
+        $store->expects('find')->never();
+        $similar = new SimilarSections(LibraryFixtures::access([], true, $store));
+        $row = self::sectionLike1055()->children()[0];
+
+        self::assertSame([], $similar->warnings((new DiviChange('eingefügt'))->record($row, 'inserted')));
+        self::assertSame([], $similar->warnings((new DiviChange('geändert'))->record(self::sectionLike1055(), 'updated')));
+    }
+
+    /** A global instance is already linked to the library – no warning, even for a global section entry. */
+    public function testGlobalInstancesDoNotWarn(): void
+    {
+        $instance = \LIT\MCP\Integrations\Divi\BlockTree\GlobalInstance::of(self::sectionLike1055(), 1055);
+        $change = (new DiviChange('eingefügt'))->record($instance, 'inserted');
+
+        self::assertSame([], self::similar()->warnings($change));
+    }
+}
diff --git a/tests/Unit/Integrations/Divi/Pages/DiviWriterTest.php b/tests/Unit/Integrations/Divi/Pages/DiviWriterTest.php
index 772cf8a..7b2c997 100644
--- a/tests/Unit/Integrations/Divi/Pages/DiviWriterTest.php
+++ b/tests/Unit/Integrations/Divi/Pages/DiviWriterTest.php
@@ -10,8 +10,10 @@ use LIT\MCP\Abilities\WriteFailed;
 use LIT\MCP\ChangeLog\ChangeLog;
 use LIT\MCP\Integrations\Divi\BlockTree\AttrMap;
 use LIT\MCP\Integrations\Divi\Design\DesignSystemReader;
+use LIT\MCP\Integrations\Divi\Library\SimilarSections;
 use LIT\MCP\Integrations\Divi\Pages\DiviChange;
 use LIT\MCP\Integrations\Divi\Pages\DiviComposition;
+use LIT\MCP\Integrations\Divi\Pages\DiviInsertAbility;
 use LIT\MCP\Integrations\Divi\Pages\DiviPage;
 use LIT\MCP\Integrations\Divi\Pages\DiviPageLoader;
 use LIT\MCP\Integrations\Divi\Pages\DiviSaver;
@@ -245,4 +247,48 @@ final class DiviWriterTest extends TestCase
         $log->assertRecorded();
         $log->assertPartials();
     }
+
+    /** Spec §5.5: the writer adds the similar-section warnings to every write result. */
+    public function testWriteResultsCarryTheSimilarSectionWarning(): void
+    {
+        $content = DiviFixtures::markup('synthetic-basic.html');
+        DiviFixtures::givenPost($content);
+        Functions\when('get_preview_post_link')->justReturn('https://kunde.test/?page_id=7&preview=true');
+        $similar = Mockery::mock(SimilarSections::class);
+        $similar->allows('warnings')->andReturn(['Ein gleich aufgebauter Abschnitt liegt in der Divi-Bibliothek.']);
+        $saved = [];
+        $failures = [];
+        $writer = DiviWriterFixture::writer($saved, $failures, false, null, null, null, $similar);
+
+        $result = (new DiviInsertAbility($writer))->execute([
+            'post_id' => 7,
+            'tree_rev' => \LIT\MCP\Abilities\Rev::of($content),
+            'nodes' => [['type' => 'section', 'modules' => [['type' => 'text', 'content' => 'Neu']]]],
+        ]);
+
+        self::assertContains('Ein gleich aufgebauter Abschnitt liegt in der Divi-Bibliothek.', $result['warnings']);
+    }
+
+    /** What lit/library-insert inserts comes from the library – no advice to use the library. */
+    public function testLibraryInsertIsNotAskedForTheSimilarSectionWarning(): void
+    {
+        $content = DiviFixtures::markup('synthetic-basic.html');
+        DiviFixtures::givenPost($content);
+        Functions\when('get_preview_post_link')->justReturn('https://kunde.test/?page_id=7&preview=true');
+        Functions\when('do_action')->justReturn(null);
+        $similar = Mockery::mock(SimilarSections::class);
+        $similar->expects('warnings')->never();
+        $saved = [];
+        $failures = [];
+        $writer = DiviWriterFixture::writer($saved, $failures, false, null, null, null, $similar);
+        $input = ['post_id' => 7, 'tree_rev' => Rev::of($content)];
+        $page = $writer->page($input);
+        $section = $page->index->find('s1')->copy();
+        $page->document->children()[0]->removeChild($page->index->find('s1'));
+        $change = (new DiviChange('eingefügt'))->record($section, 'inserted');
+
+        $result = $writer->save('lit/library-insert', $page, $change, $input);
+
+        self::assertSame(811, $result['revision_id']);
+    }
 }