diff --git a/backend/packages/harness/deerflow/community/brave/tools.py b/backend/packages/harness/deerflow/community/brave/tools.py
index 31a2370470..947a7e076b 100644
--- a/backend/packages/harness/deerflow/community/brave/tools.py
+++ b/backend/packages/harness/deerflow/community/brave/tools.py
@@ -56,7 +56,7 @@ def _coerce_max_results(
 ) -> int:
     try:
         coerced = int(value)
-    except (TypeError, ValueError):
+    except (TypeError, ValueError, OverflowError):
         logger.warning(
             "Invalid Brave Search max_results=%r; using default %s",
             value,
diff --git a/backend/packages/harness/deerflow/community/groundroute/tools.py b/backend/packages/harness/deerflow/community/groundroute/tools.py
index d8be3fdd6e..d666e03eb3 100644
--- a/backend/packages/harness/deerflow/community/groundroute/tools.py
+++ b/backend/packages/harness/deerflow/community/groundroute/tools.py
@@ -55,7 +55,7 @@ def _get_api_key(tool_name: str) -> str | None:
 def _coerce_max_results(value: object, *, default: int = _DEFAULT_MAX_RESULTS) -> int:
     try:
         coerced = int(value)
-    except (TypeError, ValueError):
+    except (TypeError, ValueError, OverflowError):
         logger.warning("Invalid GroundRoute max_results=%r; using default %s", value, default)
         coerced = default
     return max(1, min(coerced, _MAX_RESULTS_CAP))
diff --git a/backend/packages/harness/deerflow/community/searxng/tools.py b/backend/packages/harness/deerflow/community/searxng/tools.py
index 447f9726e3..9eb3e822b6 100644
--- a/backend/packages/harness/deerflow/community/searxng/tools.py
+++ b/backend/packages/harness/deerflow/community/searxng/tools.py
@@ -46,7 +46,7 @@ async def web_search_tool(query: str, time_range: SearchTimeRange | None = None)
             else:
                 try:
                     max_results = int(raw)
-                except (TypeError, ValueError):
+                except (TypeError, ValueError, OverflowError):
                     logger.warning(
                         "Invalid SearXNG max_results=%r; using default %s",
                         raw,
diff --git a/backend/packages/harness/deerflow/community/serper/tools.py b/backend/packages/harness/deerflow/community/serper/tools.py
index 9f960981dd..8ca23ab957 100644
--- a/backend/packages/harness/deerflow/community/serper/tools.py
+++ b/backend/packages/harness/deerflow/community/serper/tools.py
@@ -40,7 +40,7 @@ def _coerce_max_results(value: object, default: int = 5, max_allowed: int = _SER
     """Coerce config/parameter input into a bounded positive result count."""
     try:
         count = int(value)
-    except (TypeError, ValueError):
+    except (TypeError, ValueError, OverflowError):
         return default
     if count <= 0:
         return default
diff --git a/backend/packages/harness/deerflow/community/serply/tools.py b/backend/packages/harness/deerflow/community/serply/tools.py
index 7d476d9597..e0f65062a5 100644
--- a/backend/packages/harness/deerflow/community/serply/tools.py
+++ b/backend/packages/harness/deerflow/community/serply/tools.py
@@ -58,7 +58,7 @@ def _coerce_max_results(
 ) -> int:
     try:
         coerced = int(value)
-    except (TypeError, ValueError):
+    except (TypeError, ValueError, OverflowError):
         logger.warning("Invalid Serply max_results=%r; using default %s", value, default)
         coerced = default
     if coerced < 1:
diff --git a/backend/packages/harness/deerflow/community/sofya/tools.py b/backend/packages/harness/deerflow/community/sofya/tools.py
index 92ffcf06b8..b78ff64c7b 100644
--- a/backend/packages/harness/deerflow/community/sofya/tools.py
+++ b/backend/packages/harness/deerflow/community/sofya/tools.py
@@ -46,7 +46,7 @@ def _coerce_max_results(value: object, default: int = 5, max_allowed: int = _SOF
     """Coerce config/parameter input into a bounded positive result count."""
     try:
         count = int(value)  # type: ignore[call-overload]
-    except (TypeError, ValueError):
+    except (TypeError, ValueError, OverflowError):
         return default
     if count <= 0:
         return default
@@ -57,7 +57,7 @@ def _coerce_content_limit(value: object, default: int = _DEFAULT_CONTENTS_MAX_CH
     """Coerce the per-result content limit. 0 means no limit; anything invalid falls back to the default."""
     try:
         limit = int(value)  # type: ignore[call-overload]
-    except (TypeError, ValueError):
+    except (TypeError, ValueError, OverflowError):
         return default
     return limit if limit >= 0 else default
 
diff --git a/backend/tests/test_brave_tools.py b/backend/tests/test_brave_tools.py
index 3d57a25b21..8d04f68c9e 100644
--- a/backend/tests/test_brave_tools.py
+++ b/backend/tests/test_brave_tools.py
@@ -731,3 +731,10 @@ def test_package_exports_image_search_tool():
     from deerflow.community.brave.tools import image_search_tool as direct_image_search_tool
 
     assert image_search_tool is direct_image_search_tool
+
+
+def test_coerce_max_results_inf_falls_back_to_default():
+    """A YAML `.inf` max_results must fall back to the default, not crash."""
+    import deerflow.community.brave.tools as brave_mod
+
+    assert brave_mod._coerce_max_results(float("inf")) == brave_mod._DEFAULT_MAX_RESULTS
diff --git a/backend/tests/test_groundroute_tools.py b/backend/tests/test_groundroute_tools.py
index 71e01df261..95de840fae 100644
--- a/backend/tests/test_groundroute_tools.py
+++ b/backend/tests/test_groundroute_tools.py
@@ -328,3 +328,10 @@ class TestWebFetchTool:
             patcher.stop()
 
         assert result == "Error: No results found"
+
+
+def test_coerce_max_results_inf_falls_back_to_default():
+    """A YAML `.inf` max_results must fall back to the default, not crash."""
+    import deerflow.community.groundroute.tools as groundroute_mod
+
+    assert groundroute_mod._coerce_max_results(float("inf")) == groundroute_mod._DEFAULT_MAX_RESULTS
diff --git a/backend/tests/test_searxng_client.py b/backend/tests/test_searxng_client.py
index f3b8850270..e6b11ba32b 100644
--- a/backend/tests/test_searxng_client.py
+++ b/backend/tests/test_searxng_client.py
@@ -298,3 +298,24 @@ class TestSearxngTools:
             await tools.web_search_tool.ainvoke({"query": "latest release", "time_range": "week"})
 
         mock_client.search.assert_called_once_with("latest release", max_results=5, time_range="week")
+
+    @patch("deerflow.community.searxng.tools._get_searxng_client")
+    async def test_web_search_tool_inf_max_results_falls_back_to_default(self, mock_get_client):
+        """A YAML `.inf` max_results must fall back to the default, not error out."""
+        mock_client = MagicMock()
+        mock_client.search = AsyncMock(
+            return_value=[
+                {"title": "Result 1", "url": "https://example.com/1", "content": "Desc 1"},
+            ]
+        )
+        mock_get_client.return_value = mock_client
+
+        with patch(
+            "deerflow.community.searxng.tools._get_tool_config",
+            return_value={"max_results": float("inf")},
+        ):
+            result = await tools.web_search_tool.ainvoke("test query")
+
+        data = json.loads(result)
+        assert "error" not in data
+        assert mock_client.search.call_args.kwargs["max_results"] == 5
diff --git a/backend/tests/test_serper_tools.py b/backend/tests/test_serper_tools.py
index f1bbddc9d4..199d680364 100644
--- a/backend/tests/test_serper_tools.py
+++ b/backend/tests/test_serper_tools.py
@@ -1212,3 +1212,10 @@ def test_package_exports_image_search_tool():
     from deerflow.community.serper.tools import image_search_tool as direct_image_search_tool
 
     assert image_search_tool is direct_image_search_tool
+
+
+def test_coerce_max_results_inf_falls_back_to_default():
+    """A YAML `.inf` max_results must fall back to the default, not crash."""
+    import deerflow.community.serper.tools as serper_mod
+
+    assert serper_mod._coerce_max_results(float("inf")) == 5
diff --git a/backend/tests/test_serply_tools.py b/backend/tests/test_serply_tools.py
index 89fed878e7..557f92df31 100644
--- a/backend/tests/test_serply_tools.py
+++ b/backend/tests/test_serply_tools.py
@@ -316,3 +316,10 @@ class TestWebSearchTool:
 
         assert result["total_results"] == 1
         assert mock_get.call_args.kwargs["headers"]["X-Api-Key"] == "env-key"
+
+
+def test_coerce_max_results_inf_falls_back_to_default():
+    """A YAML `.inf` max_results must fall back to the default, not crash."""
+    import deerflow.community.serply.tools as serply_mod
+
+    assert serply_mod._coerce_max_results(float("inf")) == serply_mod._DEFAULT_MAX_RESULTS
diff --git a/backend/tests/test_sofya_tools.py b/backend/tests/test_sofya_tools.py
index fa931da283..09d91157d4 100644
--- a/backend/tests/test_sofya_tools.py
+++ b/backend/tests/test_sofya_tools.py
@@ -591,3 +591,15 @@ class TestWebFetchTool:
             result = web_fetch_tool.invoke({"url": "https://example.com"})
 
         assert result == "Error: SOFYA_API_KEY is not configured"
+
+
+class TestCoerceInfFallsBackToDefault:
+    def test_coerce_max_results_inf_returns_default(self):
+        from deerflow.community.sofya.tools import _coerce_max_results
+
+        assert _coerce_max_results(float("inf")) == 5
+
+    def test_coerce_content_limit_inf_returns_default(self):
+        from deerflow.community.sofya.tools import _coerce_content_limit
+
+        assert _coerce_content_limit(float("inf")) == 2000