diff --git a/src/lib/server/integrations/komodo.ts b/src/lib/server/integrations/komodo.ts
index a192287..b0c8de2 100644
--- a/src/lib/server/integrations/komodo.ts
+++ b/src/lib/server/integrations/komodo.ts
@@ -525,13 +525,16 @@ export type KomodoTagResult =
     | { ok: true; id: string }
     | { ok: false; message: string };
 
-// Komodo serializes Mongo ObjectIds as `_id` in the raw mongo docs and as
-// `id` in the API DTOs (rust serde default). Accept either everywhere.
+// Accept API string IDs and raw Mongo Extended JSON: { _id: { $oid: "..." } }.
 function extractTagId(t: unknown): string | null {
     if (!t || typeof t !== 'object') return null;
     const o = t as { id?: unknown; _id?: unknown };
     if (typeof o.id === 'string' && o.id.length > 0) return o.id;
     if (typeof o._id === 'string' && o._id.length > 0) return o._id;
+    if (o._id && typeof o._id === 'object') {
+        const oid = (o._id as { $oid?: unknown }).$oid;
+        if (typeof oid === 'string' && oid.length > 0) return oid;
+    }
     return null;
 }
 
diff --git a/tests/unit/komodo-tags.test.ts b/tests/unit/komodo-tags.test.ts
new file mode 100644
index 0000000..2c105c8
--- /dev/null
+++ b/tests/unit/komodo-tags.test.ts
@@ -0,0 +1,88 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { komodoEnsureTag, komodoUpdateTagsOnResource } from '../../src/lib/server/integrations/komodo.js';
+
+vi.mock('../../src/lib/server/config.js', () => ({
+    config: {
+        komodo: { address: 'http://komodo.test', apiKey: 'test', apiSecret: 'test' },
+        httpTimeoutMs: 1000
+    },
+    komodoConfigured: () => true
+}));
+
+const fetchMock = vi.fn<typeof fetch>();
+const gameId = '6aa1fb6bc27e735cc0767f5a';
+const mapId = '6aabe8567a227ba7d9aad3e9';
+const tags = [
+    { _id: { $oid: gameId }, name: 't5', owner: '6aa1e0ba91f87b7712e8caf8', color: 'Slate' },
+    { _id: { $oid: mapId }, name: 'zombie_cod5_sumpf', owner: '6aa1e0ba91f87b7712e8caf8', color: 'Slate' }
+];
+
+beforeEach(() => {
+    fetchMock.mockReset();
+    vi.stubGlobal('fetch', fetchMock);
+    vi.spyOn(console, 'warn').mockImplementation(() => {});
+});
+
+afterEach(() => {
+    vi.unstubAllGlobals();
+    vi.restoreAllMocks();
+});
+
+describe('Komodo tags', () => {
+    it('reuses the tags from the logged Mongo response and sends string IDs to the deployment', async () => {
+        fetchMock
+            .mockResolvedValueOnce(Response.json(tags))
+            .mockResolvedValueOnce(Response.json(tags))
+            .mockResolvedValueOnce(Response.json({}));
+
+        const game = await komodoEnsureTag('t5');
+        const map = await komodoEnsureTag('zombie_cod5_sumpf');
+        expect(game).toEqual({ ok: true, id: gameId });
+        expect(map).toEqual({ ok: true, id: mapId });
+        if (!game.ok || !map.ok) throw new Error('Expected both tags to resolve');
+        expect(await komodoUpdateTagsOnResource('Deployment', 't5-sumpf-1', [game.id, map.id]))
+            .toEqual({ ok: true });
+        expect(fetchMock.mock.calls.map(([url]) => url)).toEqual([
+            'http://komodo.test/read/ListTags',
+            'http://komodo.test/read/ListTags',
+            'http://komodo.test/write/UpdateTagsOnResource'
+        ]);
+        expect(JSON.parse(fetchMock.mock.calls[2][1]!.body as string)).toEqual({
+            target: { type: 'Deployment', id: 't5-sumpf-1' }, tags: [gameId, mapId]
+        });
+        expect(console.warn).not.toHaveBeenCalled();
+    });
+
+    it.each([{ id: gameId }, { _id: gameId }])('preserves string ID support: %j', async (id) => {
+        fetchMock.mockResolvedValueOnce(Response.json([{ ...id, name: 't5' }]));
+        expect(await komodoEnsureTag('t5')).toEqual({ ok: true, id: gameId });
+        expect(fetchMock).toHaveBeenCalledTimes(1);
+    });
+
+    it('reads an Extended JSON ID from CreateTag without another lookup', async () => {
+        fetchMock
+            .mockResolvedValueOnce(Response.json([]))
+            .mockResolvedValueOnce(Response.json([]))
+            .mockResolvedValueOnce(Response.json(tags[0]));
+        expect(await komodoEnsureTag('t5')).toEqual({ ok: true, id: gameId });
+        expect(fetchMock).toHaveBeenCalledTimes(3);
+        expect(fetchMock.mock.calls[2][0]).toBe('http://komodo.test/write/CreateTag');
+    });
+
+    it('recovers when another caller creates the tag after the initial lookup', async () => {
+        fetchMock
+            .mockResolvedValueOnce(Response.json([]))
+            .mockResolvedValueOnce(Response.json([]))
+            .mockResolvedValueOnce(Response.json({ error: 'E11000 duplicate key error' }, { status: 500 }))
+            .mockResolvedValueOnce(Response.json(tags));
+        expect(await komodoEnsureTag('t5')).toEqual({ ok: true, id: gameId });
+        expect(fetchMock).toHaveBeenCalledTimes(4);
+    });
+
+    it.each([null, {}, { $oid: '' }, { $oid: 123 }])('rejects malformed Mongo IDs: %j', async (_id) => {
+        fetchMock
+            .mockResolvedValueOnce(Response.json([{ name: 't5', _id }]))
+            .mockResolvedValueOnce(Response.json({ error: 'create failed' }, { status: 400 }));
+        expect(await komodoEnsureTag('t5')).toMatchObject({ ok: false });
+    });
+});