diff --git a/apps/server/src/core/ai-chat/tools/ai-chat-tools.service.ts b/apps/server/src/core/ai-chat/tools/ai-chat-tools.service.ts
index 40a079c9..f4f8c926 100644
--- a/apps/server/src/core/ai-chat/tools/ai-chat-tools.service.ts
+++ b/apps/server/src/core/ai-chat/tools/ai-chat-tools.service.ts
@@ -729,6 +729,35 @@ export class AiChatToolsService {
           }),
       ),
 
+      // Schema + description live in @docmost/mcp's SHARED_TOOL_SPECS (#423).
+      // meta.hash in the result is the baseHash drawioUpdate requires.
+      drawioGet: sharedTool(
+        sharedToolSpecs.drawioGet,
+        async ({ pageId, node, format }) =>
+          await client.drawioGet(pageId, node, format ?? 'xml'),
+      ),
+
+      // Schema + description live in @docmost/mcp's SHARED_TOOL_SPECS (#423).
+      // The flat schema fields are regrouped into the client's `where` object.
+      drawioCreate: sharedTool(
+        sharedToolSpecs.drawioCreate,
+        async ({ pageId, xml, position, anchorNodeId, anchorText, title }) =>
+          await client.drawioCreate(
+            pageId,
+            { position, anchorNodeId, anchorText },
+            xml,
+            title,
+          ),
+      ),
+
+      // Schema + description live in @docmost/mcp's SHARED_TOOL_SPECS (#423).
+      // baseHash is the optimistic lock: mismatch => structured conflict error.
+      drawioUpdate: sharedTool(
+        sharedToolSpecs.drawioUpdate,
+        async ({ pageId, node, xml, baseHash }) =>
+          await client.drawioUpdate(pageId, node, xml, baseHash),
+      ),
+
       // Schema + description now live in @docmost/mcp's SHARED_TOOL_SPECS (#294).
       // The table reference parameter was unified to `table` (was `tableRef`).
       tableInsertRow: sharedTool(
diff --git a/apps/server/src/core/ai-chat/tools/docmost-client.loader.ts b/apps/server/src/core/ai-chat/tools/docmost-client.loader.ts
index 8c8761fa..541abca3 100644
--- a/apps/server/src/core/ai-chat/tools/docmost-client.loader.ts
+++ b/apps/server/src/core/ai-chat/tools/docmost-client.loader.ts
@@ -168,6 +168,32 @@ export interface DocmostClientLike {
     url: string,
     opts?: { align?: 'left' | 'center' | 'right'; alt?: string },
   ): Promise<Record<string, unknown>>;
+  // --- draw.io diagrams (#423, stage 1) ---
+  // Read a diagram as decoded mxGraph XML (default) or the raw .drawio.svg.
+  // meta.hash is the optimistic-lock key drawioUpdate expects as baseHash.
+  drawioGet(
+    pageId: string,
+    node: string,
+    format?: 'xml' | 'svg',
+  ): Promise<Record<string, unknown>>;
+  // Lint mxGraph XML, build the .drawio.svg attachment and insert a drawio node.
+  drawioCreate(
+    pageId: string,
+    where: {
+      position: 'before' | 'after' | 'append';
+      anchorNodeId?: string;
+      anchorText?: string;
+    },
+    xml: string,
+    title?: string,
+  ): Promise<Record<string, unknown>>;
+  // Optimistic-locked full replacement of a diagram (baseHash from drawioGet).
+  drawioUpdate(
+    pageId: string,
+    node: string,
+    xml: string,
+    baseHash: string,
+  ): Promise<Record<string, unknown>>;
   tableInsertRow(
     pageId: string,
     tableRef: string,
diff --git a/packages/mcp/test/unit/client-host-contract.test.mjs b/packages/mcp/test/unit/client-host-contract.test.mjs
index edbb2f74..8d7f17d5 100644
--- a/packages/mcp/test/unit/client-host-contract.test.mjs
+++ b/packages/mcp/test/unit/client-host-contract.test.mjs
@@ -81,6 +81,10 @@ const HOST_CONTRACT_METHODS = [
   "insertImage",
   "replaceImage",
   "insertFootnote",
+  // draw.io diagrams (#423, stage 1) — read + create + optimistic-locked update
+  "drawioGet",
+  "drawioCreate",
+  "drawioUpdate",
   // write (comment)
   "createComment",
   "resolveComment",