diff --git a/mcp/server.php b/mcp/server.php
index 1c65b5d..78254c4 100644
--- a/mcp/server.php
+++ b/mcp/server.php
@@ -23,6 +23,11 @@ require_once dirname(__DIR__) . '/helpers/UrlHelper.php';
 require_once dirname(__DIR__) . '/models/UserModel.php';
 require_once dirname(__DIR__) . '/models/TicketModel.php';
 require_once dirname(__DIR__) . '/models/CommentModel.php';
+require_once dirname(__DIR__) . '/models/StatsModel.php';
+require_once dirname(__DIR__) . '/controllers/ApiTicketController.php';
+require_once dirname(__DIR__) . '/services/TicketCreationService.php';
+require_once dirname(__DIR__) . '/services/CommentService.php';
+require_once dirname(__DIR__) . '/services/AssignmentService.php';
 
 use Laminas\HttpHandlerRunner\Emitter\SapiEmitter;
 use Mcp\Server;
diff --git a/mcp/src/ToolCatalog.php b/mcp/src/ToolCatalog.php
index b09825d..41d57e0 100644
--- a/mcp/src/ToolCatalog.php
+++ b/mcp/src/ToolCatalog.php
@@ -5,6 +5,7 @@ namespace TinkerTickets\Mcp;
 use Mcp\Schema\ToolAnnotations;
 use Mcp\Server\Builder;
 use TinkerTickets\Mcp\Tools\TicketReadTools;
+use TinkerTickets\Mcp\Tools\TicketWriteTools;
 
 /**
  * The single list of MCP tools: registration, plus which ones need the
@@ -14,7 +15,7 @@ use TinkerTickets\Mcp\Tools\TicketReadTools;
 final class ToolCatalog
 {
     /** Tool names that mutate data and require tickets:write. */
-    private const WRITE_TOOLS = [];
+    private const WRITE_TOOLS = ['create_ticket', 'add_comment', 'update_status', 'assign_ticket'];
 
     public static function isWriteTool(string $name): bool
     {
@@ -24,10 +25,18 @@ final class ToolCatalog
     public static function register(Builder $builder, \mysqli $conn): Builder
     {
         $read = new TicketReadTools($conn);
+        $write = new TicketWriteTools($conn);
         $readOnly = new ToolAnnotations(readOnlyHint: true, destructiveHint: false, idempotentHint: true, openWorldHint: false);
+        // Writes change tickets (and notify people) but never delete anything.
+        $additive = new ToolAnnotations(readOnlyHint: false, destructiveHint: false, idempotentHint: false, openWorldHint: false);
+        $update = new ToolAnnotations(readOnlyHint: false, destructiveHint: false, idempotentHint: true, openWorldHint: false);
 
         return $builder
             ->addTool([$read, 'searchTickets'], 'search_tickets', 'Search tickets', null, $readOnly)
-            ->addTool([$read, 'getTicket'], 'get_ticket', 'Get ticket', null, $readOnly);
+            ->addTool([$read, 'getTicket'], 'get_ticket', 'Get ticket', null, $readOnly)
+            ->addTool([$write, 'createTicket'], 'create_ticket', 'Create ticket', null, $additive)
+            ->addTool([$write, 'addComment'], 'add_comment', 'Add comment', null, $additive)
+            ->addTool([$write, 'updateStatus'], 'update_status', 'Update ticket status', null, $update)
+            ->addTool([$write, 'assignTicket'], 'assign_ticket', 'Assign ticket', null, $update);
     }
 }
diff --git a/mcp/src/Tools/TicketWriteTools.php b/mcp/src/Tools/TicketWriteTools.php
new file mode 100644
index 0000000..2b28012
--- /dev/null
+++ b/mcp/src/Tools/TicketWriteTools.php
@@ -0,0 +1,216 @@
+<?php
+
+namespace TinkerTickets\Mcp\Tools;
+
+use Mcp\Exception\ToolCallException;
+use TinkerTickets\Mcp\Auth\McpIdentity;
+
+/**
+ * Write tools. Each one is a thin adapter over the exact code path the web UI
+ * uses (TicketCreationService, CommentService, ApiTicketController,
+ * AssignmentService), run as the signed-in user, so permissions, workflow
+ * rules, audit entries, notifications and stats-cache invalidation are
+ * identical. Gated by tickets:write in ToolScopeMiddleware (see ToolCatalog).
+ */
+final class TicketWriteTools
+{
+    private const VISIBILITIES = ['public', 'internal', 'confidential'];
+
+    public function __construct(private readonly \mysqli $conn)
+    {
+    }
+
+    /**
+     * Create a new ticket as you. It starts in the Open status.
+     *
+     * @param string      $title             Short summary of the issue.
+     * @param string      $description       Full description (markdown supported).
+     * @param int         $priority          1 (critical) to 5 (minimal). Default 4.
+     * @param string      $category          Ticket category, e.g. "General", "Hardware", "Network".
+     * @param string      $type              Ticket type, e.g. "Issue", "Task", "Request".
+     * @param string      $visibility        "public" (everyone), "internal" (only the listed groups), or "confidential" (only you, the assignee and admins).
+     * @param string|null $visibility_groups Comma-separated group names; required when visibility is "internal".
+     * @param string|null $assignee          Username to assign to, or "me". Omit to leave unassigned.
+     *
+     * @return array<string, mixed>
+     */
+    public function createTicket(
+        string $title,
+        string $description,
+        int $priority = 4,
+        string $category = 'General',
+        string $type = 'Issue',
+        string $visibility = 'public',
+        ?string $visibility_groups = null,
+        ?string $assignee = null,
+    ): array {
+        $user = McpIdentity::user();
+
+        // The web form constrains these with dropdowns; an API caller can send
+        // anything, so validate them here before handing off.
+        if ($priority < 1 || $priority > 5) {
+            throw new ToolCallException('priority must be between 1 and 5');
+        }
+        if (!in_array($visibility, self::VISIBILITIES, true)) {
+            throw new ToolCallException('visibility must be one of: ' . implode(', ', self::VISIBILITIES));
+        }
+
+        $assignedTo = null;
+        if ($assignee !== null && trim($assignee) !== '') {
+            $assignedTo = $this->resolveUserId(trim($assignee), $user);
+        }
+
+        $result = \TicketCreationService::create($this->conn, $user, [
+            'title' => $title,
+            'description' => $description,
+            'priority' => (string)$priority,
+            'category' => $category,
+            'type' => $type,
+            'status' => 'Open',
+            'visibility' => $visibility,
+            'visibility_groups' => $visibility_groups,
+            'assigned_to' => $assignedTo,
+        ]);
+        if (!$result['success']) {
+            throw new ToolCallException($result['error']);
+        }
+
+        return [
+            'ticket_id' => (string)$result['ticket_id'],
+            'url' => \UrlHelper::ticketUrl((string)$result['ticket_id']),
+        ];
+    }
+
+    /**
+     * Post a comment on a ticket as you. @username mentions notify that user.
+     *
+     * @param string   $ticket_id The ticket ID.
+     * @param string   $text      The comment text.
+     * @param bool     $markdown  Render the comment as markdown.
+     * @param int|null $reply_to  comment_id of the comment you are replying to, if any.
+     *
+     * @return array<string, mixed>
+     */
+    public function addComment(string $ticket_id, string $text, bool $markdown = true, ?int $reply_to = null): array
+    {
+        $user = McpIdentity::user();
+        $result = \CommentService::addComment($this->conn, $user, [
+            'ticket_id' => $ticket_id,
+            'comment_text' => $text,
+            'markdown_enabled' => $markdown,
+            'parent_comment_id' => $reply_to,
+        ]);
+        if (empty($result['success'])) {
+            throw new ToolCallException($this->errorMessage($result, $ticket_id));
+        }
+
+        return [
+            'comment_id' => (int)$result['comment_id'],
+            'ticket_id' => trim($ticket_id),
+            'mentions' => $result['mentions'] ?? [],
+        ];
+    }
+
+    /**
+     * Change a ticket's status. Transitions follow the Workflow Designer rules;
+     * some transitions (e.g. closing) require a comment, which is posted as the reason.
+     *
+     * @param string      $ticket_id The ticket ID.
+     * @param string      $status    New status, e.g. "Open", "Pending", "In Progress", "Closed".
+     * @param string|null $comment   Reason for the change; required for transitions that need one.
+     *
+     * @return array<string, mixed>
+     */
+    public function updateStatus(string $ticket_id, string $status, ?string $comment = null): array
+    {
+        $user = McpIdentity::user();
+        $validStatuses = $GLOBALS['config']['TICKET_STATUSES'] ?? ['Open', 'Pending', 'In Progress', 'Closed'];
+        if (!in_array($status, $validStatuses, true)) {
+            throw new ToolCallException('Unknown status. Valid statuses: ' . implode(', ', $validStatuses));
+        }
+
+        $ticketId = trim($ticket_id);
+        if (!ctype_digit($ticketId)) {
+            throw new ToolCallException("Ticket {$ticketId} not found");
+        }
+
+        $controller = new \ApiTicketController($this->conn, (int)$user['user_id'], !empty($user['is_admin']), $user);
+        $data = ['status' => $status];
+        if ($comment !== null && trim($comment) !== '') {
+            $data['comment'] = $comment;
+            $data['markdown_enabled'] = true;
+        }
+        $result = $controller->update($ticketId, $data);
+        if (empty($result['success'])) {
+            if (!empty($result['requires_comment'])) {
+                throw new ToolCallException('This status change requires a comment explaining why. Call update_status again with a comment.');
+            }
+            throw new ToolCallException($this->errorMessage($result, $ticketId));
+        }
+
+        // api/update_ticket.php invalidates the dashboard stats cache after a
+        // successful update (outside the controller); do the same here.
+        (new \StatsModel($this->conn))->invalidateCache();
+
+        return ['ticket_id' => $ticketId, 'status' => $result['status']];
+    }
+
+    /**
+     * Assign a ticket to someone, or unassign it. Only admins, the ticket's
+     * creator, or its current assignee may do this.
+     *
+     * @param string $ticket_id The ticket ID.
+     * @param string $assignee  Username to assign to, "me", or "unassigned".
+     *
+     * @return array<string, mixed>
+     */
+    public function assignTicket(string $ticket_id, string $assignee): array
+    {
+        $user = McpIdentity::user();
+        $target = trim($assignee);
+        $assignedTo = strtolower($target) === 'unassigned' || $target === ''
+            ? null
+            : $this->resolveUserId($target, $user);
+
+        $result = \AssignmentService::assign($this->conn, $user, [
+            'ticket_id' => $ticket_id,
+            'assigned_to' => $assignedTo,
+        ]);
+        if (empty($result['success'])) {
+            throw new ToolCallException($this->errorMessage($result, $ticket_id));
+        }
+
+        return ['ticket_id' => trim($ticket_id), 'assigned_to' => $assignedTo === null ? null : $target];
+    }
+
+    /**
+     * @param array<string, mixed> $user
+     */
+    private function resolveUserId(string $username, array $user): int
+    {
+        if (strtolower($username) === 'me') {
+            return (int)$user['user_id'];
+        }
+        $match = (new \UserModel($this->conn))->getUserByUsername($username);
+        if (!$match) {
+            throw new ToolCallException("Unknown user: {$username}");
+        }
+        return (int)$match['user_id'];
+    }
+
+    /**
+     * Map a shared-service failure to a tool error. A ticket the user can't
+     * see reads as "not found" (like get_ticket), never "access denied", so a
+     * restricted ticket's existence isn't revealed.
+     *
+     * @param array<string, mixed> $result
+     */
+    private function errorMessage(array $result, string $ticketId): string
+    {
+        $error = (string)($result['error'] ?? 'Request failed');
+        if (in_array($error, ['Access denied', 'Ticket not found', 'Invalid ticket ID', 'Ticket ID required'], true)) {
+            return 'Ticket ' . trim($ticketId) . ' not found';
+        }
+        return $error;
+    }
+}