diff --git a/swh/indexer/storage/__init__.py b/swh/indexer/storage/__init__.py
--- a/swh/indexer/storage/__init__.py
+++ b/swh/indexer/storage/__init__.py
@@ -253,13 +253,6 @@
         db=None,
         cur=None,
     ) -> Dict[str, int]:
-        """Add mimetypes to the storage (if conflict_update is True, this will
-           override existing data if any).
-
-        Returns:
-            A dict with the number of new elements added to the storage.
-
-        """
         check_id_duplicates(mimetypes)
         mimetypes.sort(key=lambda m: m.id)
         db.mktemp_content_mimetype(cur)
diff --git a/swh/indexer/storage/interface.py b/swh/indexer/storage/interface.py
--- a/swh/indexer/storage/interface.py
+++ b/swh/indexer/storage/interface.py
@@ -78,7 +78,8 @@
         """Add mimetypes not present in storage.
 
         Args:
-            mimetypes: mimetype rows to be added
+            mimetypes: mimetype rows to be added, with their `tool` attribute set to
+            not None.
             conflict_update: Flag to determine if we want to
             overwrite (``True``) or skip duplicates (``False``, the
             default)
@@ -94,15 +95,10 @@
         """Retrieve full content mimetype per ids.
 
         Args:
-            ids (iterable): sha1 identifier
+            ids: sha1 identifiers
 
         Yields:
-            mimetypes (iterable): dictionaries with keys:
-
-                - **id** (bytes): sha1 identifier
-                - **mimetype** (bytes): raw content's mimetype
-                - **encoding** (bytes): raw content's encoding
-                - **tool** (dict): Tool used to compute the language
+            mimetype row objects
 
         """
         ...