diff --git a/requirements-dev.txt b/requirements-dev.txt
index b86630327a7..c0b50bacbe9 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -17,6 +17,7 @@ types-requests<2.31
 types-setuptools
 types-cachetools
 types-pyvmomi
+types-networkx
 
 # testing
 pytest
diff --git a/sky/dag.py b/sky/dag.py
index 0f74484518e..3b789b96ddd 100644
--- a/sky/dag.py
+++ b/sky/dag.py
@@ -36,7 +36,7 @@ def __init__(self, name: Optional[str] = None) -> None:
         """
         self.name = name
         self._task_name_lookup: Dict[str, 'task.Task'] = {}
-        self.graph = nx.DiGraph()
+        self.graph: nx.DiGraph['task.Task'] = nx.DiGraph()
 
     @property
     def tasks(self) -> List['task.Task']:
@@ -213,7 +213,7 @@ def __exit__(self, exec_type: Any, exec_val: Any, exec_tb: Any) -> None:
 
     def __repr__(self) -> str:
         """Return a string representation of the DAG."""
-        task_info = []
+        task_info: List[str] = []
         for task in self.tasks:
             downstream = self.get_downstream(task)
             downstream_names = ','.join(
@@ -236,11 +236,10 @@ def is_chain(self) -> bool:
             True if the DAG is a linear chain, False otherwise.
         """
         nodes = list(self.graph.nodes)
-        out_degrees = [self.graph.out_degree(node) for node in nodes]
 
         return (len(nodes) <= 1 or
-                (all(degree <= 1 for degree in out_degrees) and
-                 sum(degree == 0 for degree in out_degrees) == 1))
+                (all(degree <= 1 for _, degree in self.graph.out_degree) and
+                 sum(degree == 0 for _, degree in self.graph.out_degree) == 1))
 
     def is_connected_dag(self) -> bool:
         """Check if the graph is a connected directed acyclic graph (DAG).