diff --git a/app/api/mcp/route.ts b/app/api/mcp/route.ts
index e8b51f5..b66d793 100644
--- a/app/api/mcp/route.ts
+++ b/app/api/mcp/route.ts
@@ -20,6 +20,12 @@
 import { NextResponse } from 'next/server';
 import { requireWorkspacePrincipal } from '@/lib/auth/workspace-auth';
 import { getWorkspaceBotCredentials, ensureWorkspaceProvisioned } from '@/lib/workspaces';
+import {
+  ensureWorkspaceGcsProvisioned,
+  getWorkspaceGcsState,
+  getWorkspaceGcsHmacCredentials,
+} from '@/lib/workspace-gcs';
+import { VIBN_GCS_LOCATION } from '@/lib/gcp/storage';
 import {
   deployApplication,
   getApplicationInProject,
@@ -107,6 +113,9 @@ export async function GET() {
           'domains.get',
           'domains.register',
           'domains.attach',
+          'storage.describe',
+          'storage.provision',
+          'storage.inject_env',
         ],
       },
     },
@@ -210,6 +219,13 @@ export async function POST(request: Request) {
       case 'domains.attach':
         return await toolDomainsAttach(principal, params);
 
+      case 'storage.describe':
+        return await toolStorageDescribe(principal);
+      case 'storage.provision':
+        return await toolStorageProvision(principal);
+      case 'storage.inject_env':
+        return await toolStorageInjectEnv(principal, params);
+
       default:
         return NextResponse.json(
           { error: `Unknown tool "${action}"` },
@@ -1139,3 +1155,133 @@ async function toolDomainsAttach(principal: Principal, params: Record<string, an
     );
   }
 }
+
+// ──────────────────────────────────────────────────
+// Phase 5.3: Object storage (GCS via S3-compatible HMAC)
+// ──────────────────────────────────────────────────
+
+/**
+ * Shape of the S3-compatible credentials we expose to agents.
+ *
+ * The HMAC *secret* is never returned here — only the access id and
+ * the bucket/region/endpoint. Use `storage.inject_env` to push the
+ * full `{accessId, secret}` pair into a Coolify app's env vars
+ * server-side, where the secret never leaves our network.
+ */
+function describeWorkspaceStorage(ws: {
+  slug: string;
+  gcs_default_bucket_name: string | null;
+  gcs_hmac_access_id: string | null;
+  gcp_service_account_email: string | null;
+  gcp_provision_status: string | null;
+}) {
+  return {
+    status: ws.gcp_provision_status ?? 'pending',
+    bucket: ws.gcs_default_bucket_name,
+    region: VIBN_GCS_LOCATION,
+    endpoint: 'https://storage.googleapis.com',
+    accessKeyId: ws.gcs_hmac_access_id,
+    serviceAccountEmail: ws.gcp_service_account_email,
+    note:
+      'S3-compatible credentials. Use AWS SDKs with forcePathStyle=true and this endpoint. ' +
+      'The secret access key is not returned here; call storage.inject_env to push it into a Coolify app.',
+  };
+}
+
+async function toolStorageDescribe(principal: Principal) {
+  const ws = await getWorkspaceGcsState(principal.workspace.id);
+  if (!ws) {
+    return NextResponse.json({ error: 'Workspace not found' }, { status: 404 });
+  }
+  return NextResponse.json({ result: describeWorkspaceStorage(ws) });
+}
+
+async function toolStorageProvision(principal: Principal) {
+  const result = await ensureWorkspaceGcsProvisioned(principal.workspace);
+  return NextResponse.json({ result });
+}
+
+/**
+ * Inject the workspace's storage credentials into a Coolify app as
+ * env vars, so the app can reach the bucket with any S3 SDK. The
+ * HMAC secret is read server-side and written directly to Coolify —
+ * it never transits through the agent or our API response.
+ *
+ * Envs written (all tagged is_shown_once so Coolify hides the secret
+ * in the UI after first render):
+ *   STORAGE_ENDPOINT          = https://storage.googleapis.com
+ *   STORAGE_REGION            = northamerica-northeast1
+ *   STORAGE_BUCKET            = vibn-ws-{slug}-{rand}
+ *   STORAGE_ACCESS_KEY_ID     = GOOG1E... (HMAC access id)
+ *   STORAGE_SECRET_ACCESS_KEY = ... (HMAC secret — shown-once)
+ *   STORAGE_FORCE_PATH_STYLE  = "true"  (S3 SDKs need this for GCS)
+ *
+ * Agents can override the env var prefix via `params.prefix`
+ * (e.g. "S3_" for apps that expect AWS-style names).
+ */
+async function toolStorageInjectEnv(principal: Principal, params: Record<string, any>) {
+  const projectUuid = requireCoolifyProject(principal);
+  if (projectUuid instanceof NextResponse) return projectUuid;
+  const appUuid = String(params.uuid ?? params.appUuid ?? '').trim();
+  if (!appUuid) return NextResponse.json({ error: 'Param "uuid" is required' }, { status: 400 });
+  await getApplicationInProject(appUuid, projectUuid);
+
+  const prefix = String(params.prefix ?? 'STORAGE_');
+  if (!/^[A-Z][A-Z0-9_]*$/.test(prefix)) {
+    return NextResponse.json(
+      { error: 'Param "prefix" must be uppercase ASCII (letters, digits, underscores)' },
+      { status: 400 },
+    );
+  }
+
+  const ws = await getWorkspaceGcsState(principal.workspace.id);
+  if (!ws) return NextResponse.json({ error: 'Workspace not found' }, { status: 404 });
+  if (ws.gcp_provision_status !== 'ready' || !ws.gcs_default_bucket_name) {
+    return NextResponse.json(
+      {
+        error: `Workspace storage not ready (status=${ws.gcp_provision_status}). Call storage.provision first.`,
+      },
+      { status: 409 },
+    );
+  }
+  const creds = getWorkspaceGcsHmacCredentials(ws);
+  if (!creds) {
+    return NextResponse.json(
+      { error: 'Storage HMAC secret unavailable (pre-rotation key, or decrypt failed). Rotate and retry.' },
+      { status: 409 },
+    );
+  }
+
+  const entries: Array<{ key: string; value: string; shownOnce?: boolean }> = [
+    { key: `${prefix}ENDPOINT`, value: 'https://storage.googleapis.com' },
+    { key: `${prefix}REGION`, value: VIBN_GCS_LOCATION },
+    { key: `${prefix}BUCKET`, value: ws.gcs_default_bucket_name },
+    { key: `${prefix}ACCESS_KEY_ID`, value: creds.accessId },
+    { key: `${prefix}SECRET_ACCESS_KEY`, value: creds.secret, shownOnce: true },
+    { key: `${prefix}FORCE_PATH_STYLE`, value: 'true' },
+  ];
+
+  const written: string[] = [];
+  const failed: Array<{ key: string; error: string }> = [];
+  for (const e of entries) {
+    try {
+      await upsertApplicationEnv(appUuid, {
+        key: e.key,
+        value: e.value,
+        is_shown_once: e.shownOnce ?? false,
+      });
+      written.push(e.key);
+    } catch (err) {
+      failed.push({ key: e.key, error: err instanceof Error ? err.message : String(err) });
+    }
+  }
+  return NextResponse.json({
+    result: {
+      uuid: appUuid,
+      prefix,
+      written,
+      failed: failed.length ? failed : undefined,
+      bucket: ws.gcs_default_bucket_name,
+    },
+  });
+}