diff --git a/api/services/workflow/workflow_graph.py b/api/services/workflow/workflow_graph.py
index 0770bc3..fc2be79 100644
--- a/api/services/workflow/workflow_graph.py
+++ b/api/services/workflow/workflow_graph.py
@@ -222,23 +222,26 @@ class WorkflowGraph:
 
     def _assert_start_node(self):
         errors: list[WorkflowError] = []
-        start_node = [n for n in self.nodes.values() if n.data.is_start]
-        if not start_node:
+        start_nodes = [n for n in self.nodes.values() if n.data.is_start]
+        if not start_nodes:
             errors.append(
                 WorkflowError(
                     kind=ItemKind.workflow,
                     id=None,
                     field=None,
-                    message="Workflow must have exactly one start node",
+                    message="Workflow has no start node — exactly one is required",
                 )
             )
-        elif len(start_node) > 1:
+        elif len(start_nodes) > 1:
             errors.append(
                 WorkflowError(
                     kind=ItemKind.workflow,
                     id=None,
                     field=None,
-                    message="Workflow must have exactly one start node",
+                    message=(
+                        f"Workflow has {len(start_nodes)} start nodes — "
+                        f"exactly one is required"
+                    ),
                 )
             )
         return errors
diff --git a/api/tests/dto_fixtures/multiple_start_nodes.json b/api/tests/dto_fixtures/multiple_start_nodes.json
new file mode 100644
index 0000000..facb473
--- /dev/null
+++ b/api/tests/dto_fixtures/multiple_start_nodes.json
@@ -0,0 +1,17 @@
+{
+  "nodes": [
+    {
+      "id": "s1",
+      "type": "startCall",
+      "position": {"x": 0, "y": 0},
+      "data": {"name": "Start A", "prompt": "Greet path A.", "is_start": true}
+    },
+    {
+      "id": "s2",
+      "type": "startCall",
+      "position": {"x": 0, "y": 200},
+      "data": {"name": "Start B", "prompt": "Greet path B.", "is_start": true}
+    }
+  ],
+  "edges": []
+}
diff --git a/api/tests/test_workflow_graph_constraints.py b/api/tests/test_workflow_graph_constraints.py
index a493f68..eaf57aa 100644
--- a/api/tests/test_workflow_graph_constraints.py
+++ b/api/tests/test_workflow_graph_constraints.py
@@ -72,7 +72,14 @@ _SCENARIOS = [
     (
         "no_start_node",
         ["no_start_node"],
-        ["Workflow must have exactly one start node"],
+        ["Workflow has no start node"],
+    ),
+    # Two startCall nodes — surfaced separately from no_start_node so
+    # the editor can show a count-specific message.
+    (
+        "multiple_start_nodes",
+        ["multiple_start_nodes:2"],
+        ["Workflow has 2 start nodes"],
     ),
 ]