diff --git a/backend/src/backend/jupyter.py b/backend/src/backend/jupyter.py
index bcbbc6c..a5f8094 100644
--- a/backend/src/backend/jupyter.py
+++ b/backend/src/backend/jupyter.py
@@ -25,14 +25,19 @@ def extract_notebook_path(
 ) -> Optional[str]:
     """Pull the relative notebook path out of the original request URI.
 
-    Only ``/jupyter/{workspace_id}/notebooks/*.ipynb`` requests are
-    subject to file-level lock checks; everything else (tree views,
-    ``/api/contents`` and WebSocket upgrades) bypasses the lock.
+    Match ``/jupyter/{workspace_id}/notebooks/*.ipynb`` (the legacy
+    iframe flow) and ``/jupyter/{workspace_id}/api/contents/*.ipynb``
+    (the Monaco-based Contents API PUT path). The caller decides
+    whether to actually enforce the lock — typically only on writes.
     """
-    pattern = rf"^/jupyter/{re.escape(workspace_id)}/notebooks/(.+\.ipynb)"
-    match = re.match(pattern, uri)
-    if match:
-        return match.group(1)
+    nb_pattern = rf"^/jupyter/{re.escape(workspace_id)}/notebooks/(.+\.ipynb)"
+    contents_pattern = (
+        rf"^/jupyter/{re.escape(workspace_id)}/api/contents/(.+\.ipynb)"
+    )
+    for pattern in (nb_pattern, contents_pattern):
+        match = re.match(pattern, uri)
+        if match:
+            return match.group(1)
     return None
 
 
@@ -126,13 +131,16 @@ async def verify_jupyter_access(
     await load_active_membership_or_403(session, user_id, workspace_id)
 
     notebook_path = extract_notebook_path(original_uri, workspace_id)
-    if notebook_path and await check_notebook_is_locked(
-        session, workspace_id, notebook_path, user_id,
-    ):
-        raise HTTPException(
-            status_code=403,
-            detail=f"Notebook '{notebook_path}' is currently locked",
-        )
+    # Lock only on writes — reads (GET) stay open so anyone can still
+    # preview a locked notebook the way they could via the iframe before.
+    if notebook_path and request.method in {"PUT", "POST", "PATCH", "DELETE"}:
+        if await check_notebook_is_locked(
+            session, workspace_id, notebook_path, user_id,
+        ):
+            raise HTTPException(
+                status_code=403,
+                detail=f"Notebook '{notebook_path}' is currently locked",
+            )
 
     runtime_client = request.app.state.runtime_client
     ws_info = await runtime_client.get_workspace(workspace_id)