diff --git a/config/services.yaml b/config/services.yaml
index b0f5649..497cda6 100644
--- a/config/services.yaml
+++ b/config/services.yaml
@@ -45,6 +45,10 @@ services:
         arguments:
             $uploadDir: '%task_document_upload_dir%'
 
+    App\Mcp\Tool\Task\AddTaskDocumentTool:
+        arguments:
+            $uploadDir: '%task_document_upload_dir%'
+
     App\Controller\UserAvatarController:
         arguments:
             $avatarUploadDir: '%avatar_upload_dir%'
diff --git a/src/Mcp/Tool/Task/AddTaskDocumentTool.php b/src/Mcp/Tool/Task/AddTaskDocumentTool.php
new file mode 100644
index 0000000..e879d3b
--- /dev/null
+++ b/src/Mcp/Tool/Task/AddTaskDocumentTool.php
@@ -0,0 +1,110 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Mcp\Tool\Task;
+
+use App\Entity\TaskDocument;
+use App\Repository\TaskRepository;
+use DateTimeImmutable;
+use Doctrine\ORM\EntityManagerInterface;
+use InvalidArgumentException;
+use Mcp\Capability\Attribute\McpTool;
+use Symfony\Bundle\SecurityBundle\Security;
+use Symfony\Component\Security\Core\Exception\AccessDeniedException;
+use Symfony\Component\Uid\Uuid;
+
+use function sprintf;
+use function strlen;
+
+#[McpTool(name: 'add-task-document', description: 'Attach a text document (Markdown by default) to a task by passing its raw content. Optimized for Markdown reports/notes: the content is written verbatim as a UTF-8 file, no base64 needed. The MIME type is inferred from the fileName extension (.md, .txt, .csv, .json, .xml), defaulting to text/markdown.')]
+class AddTaskDocumentTool
+{
+    private const MAX_CONTENT_SIZE = 5 * 1024 * 1024; // 5 MB of text
+
+    private const EXTENSION_TO_MIME = [
+        'md'       => 'text/markdown',
+        'markdown' => 'text/markdown',
+        'txt'      => 'text/plain',
+        'csv'      => 'text/csv',
+        'json'     => 'application/json',
+        'xml'      => 'text/xml',
+    ];
+
+    public function __construct(
+        private readonly EntityManagerInterface $entityManager,
+        private readonly TaskRepository $taskRepository,
+        private readonly Security $security,
+        private readonly string $uploadDir,
+    ) {}
+
+    /**
+     * @param int    $taskId   ID of the task to attach the document to
+     * @param string $content  Raw text content of the document (e.g. Markdown)
+     * @param string $fileName Display name of the document, including extension (defaults to "document.md")
+     */
+    public function __invoke(
+        int $taskId,
+        string $content,
+        string $fileName = 'document.md',
+    ): string {
+        if (!$this->security->isGranted('ROLE_USER')) {
+            throw new AccessDeniedException('Access denied: ROLE_USER required.');
+        }
+
+        $task = $this->taskRepository->find($taskId);
+        if (null === $task) {
+            throw new InvalidArgumentException(sprintf('Task with ID %d not found.', $taskId));
+        }
+
+        if ('' === $content) {
+            throw new InvalidArgumentException('Document content cannot be empty.');
+        }
+
+        $size = strlen($content);
+        if ($size > self::MAX_CONTENT_SIZE) {
+            throw new InvalidArgumentException('Content size exceeds 5 MB limit.');
+        }
+
+        $originalName = '' !== trim($fileName) ? trim($fileName) : 'document.md';
+
+        $extension = strtolower(pathinfo($originalName, PATHINFO_EXTENSION));
+        $mimeType  = self::EXTENSION_TO_MIME[$extension] ?? 'text/markdown';
+        if ('' === $extension) {
+            $originalName .= '.md';
+            $extension = 'md';
+        }
+
+        $storedName = Uuid::v4()->toRfc4122().'.'.$extension;
+
+        if (!is_dir($this->uploadDir) && !mkdir($this->uploadDir, 0o775, true) && !is_dir($this->uploadDir)) {
+            throw new InvalidArgumentException(sprintf('Upload directory "%s" could not be created.', $this->uploadDir));
+        }
+
+        if (false === file_put_contents($this->uploadDir.'/'.$storedName, $content)) {
+            throw new InvalidArgumentException('Failed to write document to disk.');
+        }
+
+        $document = new TaskDocument();
+        $document->setTask($task);
+        $document->setOriginalName($originalName);
+        $document->setFileName($storedName);
+        $document->setMimeType($mimeType);
+        $document->setSize($size);
+        $document->setCreatedAt(new DateTimeImmutable());
+        $document->setUploadedBy($this->security->getUser());
+
+        $this->entityManager->persist($document);
+        $this->entityManager->flush();
+
+        return json_encode([
+            'id'           => $document->getId(),
+            'taskId'       => $task->getId(),
+            'originalName' => $document->getOriginalName(),
+            'mimeType'     => $document->getMimeType(),
+            'size'         => $document->getSize(),
+            'createdAt'    => $document->getCreatedAt()?->format('c'),
+            'uploadedBy'   => $document->getUploadedBy()?->getUsername(),
+        ]);
+    }
+}