diff --git a/libs/core/langchain_core/output_parsers/openai_tools.py b/libs/core/langchain_core/output_parsers/openai_tools.py
index 0b756c41491..c42e0946653 100644
--- a/libs/core/langchain_core/output_parsers/openai_tools.py
+++ b/libs/core/langchain_core/output_parsers/openai_tools.py
@@ -355,8 +355,18 @@ class PydanticToolsParser(JsonOutputToolsParser):
                     f"{res['args']}"
                 )
                 raise ValueError(msg)
+
             try:
-                pydantic_objects.append(name_dict[res["type"]](**res["args"]))
+                tool = name_dict[res["type"]]
+            except KeyError as e:
+                available = ", ".join(name_dict.keys()) or "<no_tools>"
+                msg = (
+                    f"Unknown tool type: {res['type']!r}. Available tools: {available}"
+                )
+                raise OutputParserException(msg) from e
+
+            try:
+                pydantic_objects.append(tool(**res["args"]))
             except (ValidationError, ValueError):
                 if partial:
                     continue
diff --git a/libs/core/tests/unit_tests/output_parsers/test_openai_tools.py b/libs/core/tests/unit_tests/output_parsers/test_openai_tools.py
index f2e3a475b4a..849f2a2a2c6 100644
--- a/libs/core/tests/unit_tests/output_parsers/test_openai_tools.py
+++ b/libs/core/tests/unit_tests/output_parsers/test_openai_tools.py
@@ -6,6 +6,7 @@ import pydantic
 import pytest
 from pydantic import BaseModel, Field, ValidationError
 
+from langchain_core.exceptions import OutputParserException
 from langchain_core.messages import (
     AIMessage,
     AIMessageChunk,
@@ -1423,3 +1424,31 @@ def test_parse_tool_call_partial_mode_with_none_arguments() -> None:
 
     # In partial mode, None arguments returns None (incomplete tool call)
     assert result is None
+
+
+@pytest.mark.parametrize("partial", [False, True])
+def test_pydantic_tools_parser_unknown_tool_raises_output_parser_exception(
+    partial: bool,  # noqa: FBT001
+) -> None:
+    class KnownTool(BaseModel):
+        value: int
+
+    parser = PydanticToolsParser(tools=[KnownTool])
+    message = AIMessage(
+        content="",
+        tool_calls=[
+            {
+                "id": "call_unknown",
+                "name": "UnknownTool",
+                "args": {"value": 1},
+            }
+        ],
+    )
+    generation = ChatGeneration(message=message)
+
+    with pytest.raises(OutputParserException) as excinfo:
+        parser.parse_result([generation], partial=partial)
+
+    msg = str(excinfo.value)
+    assert "Unknown tool type" in msg
+    assert "UnknownTool" in msg