fix(langgraph): keep only name, description and forked in __subagents

libs/langgraph/langgraph/pregel/_draw.py

@@ -232,6 +232,8 @@ def draw_graph(
         tools_by_name = getattr(node.bound, "tools_by_name", None)
         if isinstance(tools_by_name, Mapping) and tools_by_name:
             metadata["__tools"] = list(tools_by_name)
+            if subagents := _get_tool_subagents(tools_by_name):
+                metadata["__subagents"] = subagents
         graph.add_node(node.bound, name, metadata=metadata or None)
     # add start node
     if START not in nodes:
@@ -281,6 +283,38 @@ def draw_graph(
     return graph
 
 
+def _get_tool_subagents(
+    tools_by_name: Mapping[str, Any],
+) -> dict[str, list[dict[str, Any]]]:
+    """Collect the subagents each tool can run, keyed by tool name."""
+    subagents: dict[str, list[dict[str, Any]]] = {}
+    for tool_name, tool in tools_by_name.items():
+        tool_subagents = getattr(tool, "subagents", None)
+        if (
+            isinstance(tool_subagents, Sequence)
+            and not isinstance(tool_subagents, str)
+            and tool_subagents
+            and all(
+                isinstance(subagent, Mapping) and isinstance(subagent.get("name"), str)
+                for subagent in tool_subagents
+            )
+        ):
+            subagents[tool_name] = [
+                _subagent_entry(subagent) for subagent in tool_subagents
+            ]
+    return subagents
+
+
+def _subagent_entry(subagent: Mapping[str, Any]) -> dict[str, Any]:
+    """Keep only the subagent fields graph viewers display."""
+    entry: dict[str, Any] = {"name": subagent["name"]}
+    if isinstance(description := subagent.get("description"), str):
+        entry["description"] = description
+    if subagent.get("forked") is True:
+        entry["forked"] = True
+    return entry
+
+
 def add_edge(
     graph: Graph,
     source: str,

libs/langgraph/tests/test_pregel.py

@@ -36,7 +36,7 @@ from langchain_core.runnables import (
     RunnablePassthrough,
 )
 from langchain_core.runnables.graph import Edge
-from langchain_core.tools import tool
+from langchain_core.tools import StructuredTool, tool
 from langchain_core.version import VERSION as LANGCHAIN_CORE_VERSION
 from langgraph.cache.base import BaseCache
 from langgraph.checkpoint.base import (
@@ -3105,6 +3105,49 @@ def test_simple_multi_edge(snapshot: SnapshotAssertion) -> None:
     )
 
 
+def test_tool_node_lists_tool_subagents_in_graph_metadata() -> None:
+    class TaskTool(StructuredTool):
+        subagents: list[dict[str, Any]] = []
+
+    def run_task(description: str, subagent_type: str) -> str:
+        return subagent_type
+
+    task = TaskTool.from_function(run_task, name="task", description="Run a subagent.")
+    task.subagents = [
+        {"name": "researcher", "description": "Researches a topic."},
+        {
+            "name": "critic",
+            "description": "Reviews drafts.",
+            "forked": True,
+            "system_prompt": "You are a critic.",
+            "runnable": object(),
+        },
+        {"name": "planner", "description": None, "forked": "yes"},
+    ]
+
+    @tool
+    def search(query: str) -> str:
+        """Search the web."""
+        return query
+
+    builder = StateGraph(MessagesState)
+    builder.add_node("agent", lambda state: state)
+    builder.add_node("tools", ToolNode([search, task]))
+    builder.add_edge(START, "agent")
+    builder.add_edge("agent", "tools")
+    graph = builder.compile().get_graph().to_json()
+    nodes = {node["id"]: node for node in graph["nodes"]}
+
+    assert nodes["tools"]["metadata"]["__subagents"] == {
+        "task": [
+            {"name": "researcher", "description": "Researches a topic."},
+            {"name": "critic", "description": "Reviews drafts.", "forked": True},
+            {"name": "planner"},
+        ]
+    }
+    assert "__subagents" not in (nodes["agent"].get("metadata") or {})
+
+
 def test_nested_graph_xray(snapshot: SnapshotAssertion) -> None:
     class State(TypedDict):
         my_key: Annotated[str, operator.add]