diff --git a/src/agent_tools.py b/src/agent_tools.py
index 9a54ab8..2785623 100644
--- a/src/agent_tools.py
+++ b/src/agent_tools.py
@@ -80,6 +80,11 @@ def get_mcp_manager():
 # Helpers (kept here — used by sub-modules)
 # ---------------------------------------------------------------------------
 def _truncate(text: str, limit: int = MAX_OUTPUT_CHARS) -> str:
+    # Callers treat the result as text, so always return a string: coerce a
+    # non-string (None -> "", otherwise str(...)) instead of returning it raw,
+    # which would just move the crash downstream.
+    if not isinstance(text, str):
+        text = "" if text is None else str(text)
     if len(text) > limit:
         return text[:limit] + f"\n... (truncated, {len(text)} chars total)"
     return text
diff --git a/tests/test_agent_tools_truncate_nonstring.py b/tests/test_agent_tools_truncate_nonstring.py
new file mode 100644
index 0000000..3963217
--- /dev/null
+++ b/tests/test_agent_tools_truncate_nonstring.py
@@ -0,0 +1,24 @@
+"""Regression: agent_tools._truncate must always return a string.
+
+It did `len(text)` directly, so `_truncate(None)` raised TypeError. Returning
+the raw non-string just moves the crash downstream (callers treat it as text),
+so non-strings are now coerced to a string and still truncated.
+"""
+from src.agent_tools import _truncate
+
+
+def test_non_string_coerced_to_string():
+    assert _truncate(None) == ""
+    assert _truncate(123) == "123"
+    assert isinstance(_truncate({"a": 1}), str)
+
+
+def test_non_string_is_also_truncated():
+    out = _truncate(12345, limit=3)
+    assert out.startswith("123") and "truncated" in out
+
+
+def test_string_truncation_unchanged():
+    assert _truncate("hello", limit=100) == "hello"
+    out = _truncate("x" * 50, limit=10)
+    assert out.startswith("x" * 10) and "truncated" in out