diff --git a/src/google/adk/workflow/_tool_node.py b/src/google/adk/workflow/_tool_node.py
index fad28bb714..a007ce08c1 100644
--- a/src/google/adk/workflow/_tool_node.py
+++ b/src/google/adk/workflow/_tool_node.py
@@ -66,7 +66,24 @@ async def _run_impl(
         function_call_id=str(uuid.uuid4()),
     )
 
+    import json
+
+    from google.genai import types
+
+    from ..utils.content_utils import extract_text_from_content
+
     args = node_input
+    if isinstance(args, types.Content):
+      args = extract_text_from_content(args)
+
+    if isinstance(args, str):
+      args = args.strip()
+      if args:
+        try:
+          args = json.loads(args)
+        except json.JSONDecodeError:
+          pass
+
     if args is None:
       args = {}
     elif not isinstance(args, dict):
diff --git a/tests/unittests/workflow/test_tool_node.py b/tests/unittests/workflow/test_tool_node.py
new file mode 100644
index 0000000000..7a6ccf3ed8
--- /dev/null
+++ b/tests/unittests/workflow/test_tool_node.py
@@ -0,0 +1,133 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Tests for ToolNode input parsing and execution."""
+
+from typing import Any
+
+from google.adk.events.event import Event
+from google.adk.tools.base_tool import BaseTool
+from google.adk.workflow import START
+from google.adk.workflow._tool_node import _ToolNode as ToolNode
+from google.adk.workflow._workflow import Workflow
+from google.genai import types
+import pytest
+
+from . import workflow_testing_utils
+from .. import testing_utils
+
+
+class MockTool(BaseTool):
+  """A mock tool that returns the args it was called with."""
+
+  def __init__(self, name="mock_tool", description="Mock tool"):
+    super().__init__(name=name, description=description)
+
+  async def run_async(self, *, args: dict[str, Any], tool_context) -> Any:
+    return args
+
+
+async def _run_tool_node_wf(node_input: Any) -> list[Any]:
+  """Runs a workflow with a ToolNode that receives node_input."""
+  tool_node = ToolNode(tool=MockTool())
+
+  def start_node():
+    return Event(output=node_input)
+
+  wf = Workflow(
+      name="tool_node_test_wf",
+      edges=[
+          (START, start_node),
+          (start_node, tool_node),
+      ],
+  )
+  app_instance = testing_utils.App(name="test_app", root_agent=wf)
+  runner = testing_utils.InMemoryRunner(app=app_instance)
+  events = await runner.run_async("start")
+  return workflow_testing_utils.simplify_events_with_node(events)
+
+
+@pytest.mark.asyncio
+async def test_tool_node_accepts_dict():
+  """Tests that ToolNode accepts a dict as input and passes it to the tool."""
+  input_dict = {"param_a": 1, "param_b": "value"}
+  simplified = await _run_tool_node_wf(input_dict)
+  assert (
+      "tool_node_test_wf@1/mock_tool@1",
+      {"output": input_dict},
+  ) in simplified
+
+
+@pytest.mark.asyncio
+async def test_tool_node_accepts_none():
+  """Tests that ToolNode accepts None, converting it to an empty dict."""
+  simplified = await _run_tool_node_wf(None)
+  assert ("tool_node_test_wf@1/mock_tool@1", {"output": {}}) in simplified
+
+
+@pytest.mark.asyncio
+async def test_tool_node_accepts_json_string():
+  """Tests that ToolNode accepts a valid JSON string representing a dict."""
+  json_str = '{"param_a": 1, "param_b": "value"}'
+  simplified = await _run_tool_node_wf(json_str)
+  assert (
+      "tool_node_test_wf@1/mock_tool@1",
+      {"output": {"param_a": 1, "param_b": "value"}},
+  ) in simplified
+
+
+@pytest.mark.asyncio
+async def test_tool_node_accepts_content_with_json_string():
+  """Tests that ToolNode accepts a types.Content containing a JSON string."""
+  json_str = '{"param_a": 1, "param_b": "value"}'
+  content = types.Content(
+      parts=[types.Part.from_text(text=json_str)], role="user"
+  )
+  simplified = await _run_tool_node_wf(content)
+  assert (
+      "tool_node_test_wf@1/mock_tool@1",
+      {"output": {"param_a": 1, "param_b": "value"}},
+  ) in simplified
+
+
+@pytest.mark.asyncio
+async def test_tool_node_rejects_non_dict_json_string():
+  """Tests that ToolNode raises TypeError if JSON string represents a non-dict (e.g. list)."""
+  json_str = "[1, 2, 3]"
+  with pytest.raises(
+      TypeError, match="The input to ToolNode must be a dictionary"
+  ):
+    await _run_tool_node_wf(json_str)
+
+
+@pytest.mark.asyncio
+async def test_tool_node_rejects_invalid_json_string():
+  """Tests that ToolNode raises TypeError if string input is not valid JSON."""
+  invalid_str = "not a json"
+  with pytest.raises(
+      TypeError, match="The input to ToolNode must be a dictionary"
+  ):
+    await _run_tool_node_wf(invalid_str)
+
+
+@pytest.mark.asyncio
+async def test_tool_node_rejects_non_dict_content():
+  """Tests that ToolNode raises TypeError if Content contains non-dict text."""
+  content = types.Content(
+      parts=[types.Part.from_text(text="not a json")], role="user"
+  )
+  with pytest.raises(
+      TypeError, match="The input to ToolNode must be a dictionary"
+  ):
+    await _run_tool_node_wf(content)