diff --git a/nanobot/agent/tools/base.py b/nanobot/agent/tools/base.py
index 46cc4b472..02445b15f 100644
--- a/nanobot/agent/tools/base.py
+++ b/nanobot/agent/tools/base.py
@@ -1,6 +1,7 @@
 """Base class for agent tools."""
 from __future__ import annotations
 
+import math
 import typing
 from abc import ABC, abstractmethod
 from collections.abc import Callable
@@ -67,6 +68,8 @@ class Schema(ABC):
             return [f"{label} should be number"]
         if t in _JSON_TYPE_MAP and t not in ("integer", "number") and not isinstance(val, _JSON_TYPE_MAP[t]):
             return [f"{label} should be {t}"]
+        if t == "number" and isinstance(val, float) and not math.isfinite(val):
+            return [f"{label} must be finite"]
 
         errors: list[str] = []
         if "enum" in schema and val not in schema["enum"]:
diff --git a/tests/tools/test_tool_validation.py b/tests/tools/test_tool_validation.py
index fdb881f45..f461ccf3b 100644
--- a/tests/tools/test_tool_validation.py
+++ b/tests/tools/test_tool_validation.py
@@ -598,6 +598,24 @@ def test_cast_params_invalid_string_to_number() -> None:
     assert result["rate"] == "not_a_number"
 
 
+@pytest.mark.parametrize(
+    "value",
+    [float("nan"), float("inf"), float("-inf"), "NaN", "Infinity", "-Infinity"],
+)
+def test_cast_params_rejects_non_finite_numbers(value: float | str) -> None:
+    """JSON number parameters must remain finite after schema-driven casting."""
+    tool = CastTestTool(
+        {
+            "type": "object",
+            "properties": {"rate": {"type": "number"}},
+        }
+    )
+
+    result = tool.cast_params({"rate": value})
+
+    assert tool.validate_params(result) == ["rate must be finite"]
+
+
 def test_validate_params_bool_not_accepted_as_number() -> None:
     """Booleans should not pass number validation."""
     tool = CastTestTool(