diff --git a/swh/vault/in_memory_backend.py b/swh/vault/in_memory_backend.py
new file mode 100644
--- /dev/null
+++ b/swh/vault/in_memory_backend.py
@@ -0,0 +1,53 @@
+# Copyright (C) 2017-2021  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from typing import Any, Dict, List, Optional, Tuple, Union
+
+from swh.model.hashutil import hash_to_bytes
+
+from .cache import VaultCache
+
+ObjectId = Union[str, bytes]
+
+
+class InMemoryVaultBackend:
+    """Stub vault backend, for use in the CLI."""
+
+    def __init__(self):
+        self._cache = VaultCache(cls="memory")
+
+    def fetch(self, obj_type: str, obj_id: ObjectId) -> Optional[bytes]:
+        return self._cache.get(obj_type, obj_id)
+
+    def cook(
+        self, obj_type: str, obj_id: ObjectId, email: Optional[str] = None
+    ) -> Dict[str, Any]:
+        raise NotImplementedError("InMemoryVaultBackend.cook()")
+
+    def progress(self, obj_type: str, obj_id: ObjectId):
+        raise NotImplementedError("InMemoryVaultBackend.progress()")
+
+    # Cookers endpoints
+
+    def set_progress(self, obj_type: str, obj_id: ObjectId, progress: str) -> None:
+        pass
+
+    def set_status(self, obj_type: str, obj_id: ObjectId, status: str) -> None:
+        pass
+
+    def put_bundle(self, obj_type: str, obj_id: ObjectId, bundle) -> bool:
+        self._cache.add(obj_type, hash_to_bytes(obj_id), bundle)
+        return True
+
+    def send_notif(self, obj_type: str, obj_id: ObjectId):
+        pass
+
+    # Batch endpoints
+
+    def batch_cook(self, batch: List[Tuple[str, str]]) -> int:
+        raise NotImplementedError("InMemoryVaultBackend.batch_cook()")
+
+    def batch_progress(self, batch_id: int) -> Dict[str, Any]:
+        pass