feat: enhance JSON argument parsing and validation in CrewAgentExecutor and BaseTool

- Added error handling for malformed JSON tool arguments in CrewAgentExecutor, providing descriptive error messages.
- Implemented schema validation for tool arguments in BaseTool, ensuring that invalid arguments raise appropriate exceptions.
- Introduced tests to verify correct behavior for both valid and invalid JSON inputs, enhancing robustness of tool execution.

lib/crewai/src/crewai/agents/crew_agent_executor.py

@@ -894,11 +894,16 @@ class CrewAgentExecutor(CrewAgentExecutorMixin):
             ToolUsageStartedEvent,
         )
 
+        json_parse_error: str | None = None
         if isinstance(func_args, str):
             try:
                 args_dict = json.loads(func_args)
-            except json.JSONDecodeError:
+            except json.JSONDecodeError as e:
                 args_dict = {}
+                json_parse_error = (
+                    f"Error: Failed to parse tool arguments as JSON: {e}. "
+                    f"Please provide valid JSON arguments for the '{func_name}' tool."
+                )
         else:
             args_dict = func_args
 
@@ -980,7 +985,9 @@ class CrewAgentExecutor(CrewAgentExecutorMixin):
                     color="red",
                 )
 
-        if hook_blocked:
+        if json_parse_error:
+            result = json_parse_error
+        elif hook_blocked:
             result = f"Tool execution blocked by hook. Tool: {func_name}"
         elif max_usage_reached and original_tool:
             result = f"Tool '{func_name}' has reached its usage limit of {original_tool.max_usage_count} times and cannot be used anymore."

lib/crewai/src/crewai/tools/base_tool.py

@@ -155,9 +155,17 @@ class BaseTool(BaseModel, ABC):
         *args: Any,
         **kwargs: Any,
     ) -> Any:
+        if kwargs and self.args_schema is not None and self.args_schema.model_fields:
+            try:
+                validated = self.args_schema.model_validate(kwargs)
+                kwargs = validated.model_dump()
+            except Exception as e:
+                raise ValueError(
+                    f"Tool '{self.name}' arguments validation failed: {e}"
+                ) from e
+
         result = self._run(*args, **kwargs)
 
-        # If _run is async, we safely run it
         if asyncio.iscoroutine(result):
             result = asyncio.run(result)
 
@@ -331,6 +339,15 @@ class Tool(BaseTool, Generic[P, R]):
         Returns:
             The result of the tool execution.
         """
+        if kwargs and self.args_schema is not None and self.args_schema.model_fields:
+            try:
+                validated = self.args_schema.model_validate(kwargs)
+                kwargs = validated.model_dump()
+            except Exception as e:
+                raise ValueError(
+                    f"Tool '{self.name}' arguments validation failed: {e}"
+                ) from e
+
         result = self.func(*args, **kwargs)
 
         if asyncio.iscoroutine(result):

lib/crewai/tests/agents/test_native_tool_calling.py

@@ -11,7 +11,7 @@ import os
 import threading
 import time
 from collections import Counter
-from unittest.mock import patch
+from unittest.mock import Mock, patch
 
 import pytest
 from pydantic import BaseModel, Field
@@ -1129,3 +1129,150 @@ class TestMaxUsageCountWithNativeToolCalling:
         # Verify the requested calls occurred while keeping usage bounded.
         assert tool.current_usage_count >= 2
         assert tool.current_usage_count <= tool.max_usage_count
+
+
+# =============================================================================
+# JSON Parse Error Handling Tests
+# =============================================================================
+
+
+class TestNativeToolCallingJsonParseError:
+    """Tests that malformed JSON tool arguments produce clear errors
+    instead of silently dropping all arguments."""
+
+    def _make_executor(self, tools: list[BaseTool]) -> "CrewAgentExecutor":
+        """Create a minimal CrewAgentExecutor with mocked dependencies."""
+        from crewai.agents.crew_agent_executor import CrewAgentExecutor
+        from crewai.tools.base_tool import to_langchain
+
+        structured_tools = to_langchain(tools)
+        mock_agent = Mock()
+        mock_agent.key = "test_agent"
+        mock_agent.role = "tester"
+        mock_agent.verbose = False
+        mock_agent.fingerprint = None
+        mock_agent.tools_results = []
+
+        mock_task = Mock()
+        mock_task.name = "test"
+        mock_task.description = "test"
+        mock_task.id = "test-id"
+
+        executor = object.__new__(CrewAgentExecutor)
+        executor.agent = mock_agent
+        executor.task = mock_task
+        executor.crew = Mock()
+        executor.tools = structured_tools
+        executor.original_tools = tools
+        executor.tools_handler = None
+        executor._printer = Mock()
+        executor.messages = []
+
+        return executor
+
+    def test_malformed_json_returns_parse_error(self) -> None:
+        """Malformed JSON args must return a descriptive error, not silently become {}."""
+
+        class CodeTool(BaseTool):
+            name: str = "execute_code"
+            description: str = "Run code"
+
+            def _run(self, code: str) -> str:
+                return f"ran: {code}"
+
+        tool = CodeTool()
+        executor = self._make_executor([tool])
+
+        from crewai.utilities.agent_utils import convert_tools_to_openai_schema
+        _, available_functions = convert_tools_to_openai_schema([tool])
+
+        malformed_json = '{"code": "print("hello")"}'
+
+        result = executor._execute_single_native_tool_call(
+            call_id="call_123",
+            func_name="execute_code",
+            func_args=malformed_json,
+            available_functions=available_functions,
+        )
+
+        assert "Failed to parse tool arguments as JSON" in result["result"]
+        assert tool.current_usage_count == 0
+
+    def test_valid_json_still_executes_normally(self) -> None:
+        """Valid JSON args should execute the tool as before."""
+
+        class CodeTool(BaseTool):
+            name: str = "execute_code"
+            description: str = "Run code"
+
+            def _run(self, code: str) -> str:
+                return f"ran: {code}"
+
+        tool = CodeTool()
+        executor = self._make_executor([tool])
+
+        from crewai.utilities.agent_utils import convert_tools_to_openai_schema
+        _, available_functions = convert_tools_to_openai_schema([tool])
+
+        valid_json = '{"code": "print(1)"}'
+
+        result = executor._execute_single_native_tool_call(
+            call_id="call_456",
+            func_name="execute_code",
+            func_args=valid_json,
+            available_functions=available_functions,
+        )
+
+        assert result["result"] == "ran: print(1)"
+
+    def test_dict_args_bypass_json_parsing(self) -> None:
+        """When func_args is already a dict, no JSON parsing occurs."""
+
+        class CodeTool(BaseTool):
+            name: str = "execute_code"
+            description: str = "Run code"
+
+            def _run(self, code: str) -> str:
+                return f"ran: {code}"
+
+        tool = CodeTool()
+        executor = self._make_executor([tool])
+
+        from crewai.utilities.agent_utils import convert_tools_to_openai_schema
+        _, available_functions = convert_tools_to_openai_schema([tool])
+
+        result = executor._execute_single_native_tool_call(
+            call_id="call_789",
+            func_name="execute_code",
+            func_args={"code": "x = 42"},
+            available_functions=available_functions,
+        )
+
+        assert result["result"] == "ran: x = 42"
+
+    def test_schema_validation_catches_missing_args_on_native_path(self) -> None:
+        """The native function calling path should now enforce args_schema,
+        catching missing required fields before _run is called."""
+
+        class StrictTool(BaseTool):
+            name: str = "strict_tool"
+            description: str = "A tool with required args"
+
+            def _run(self, code: str, language: str) -> str:
+                return f"{language}: {code}"
+
+        tool = StrictTool()
+        executor = self._make_executor([tool])
+
+        from crewai.utilities.agent_utils import convert_tools_to_openai_schema
+        _, available_functions = convert_tools_to_openai_schema([tool])
+
+        result = executor._execute_single_native_tool_call(
+            call_id="call_schema",
+            func_name="strict_tool",
+            func_args={"code": "print(1)"},
+            available_functions=available_functions,
+        )
+
+        assert "Error" in result["result"]
+        assert "validation failed" in result["result"].lower() or "missing" in result["result"].lower()

lib/crewai/tests/tools/test_base_tool.py

@@ -3,6 +3,8 @@ from typing import Callable
 from unittest.mock import patch
 
 import pytest
+from pydantic import BaseModel, Field
+
 from crewai.agent import Agent
 from crewai.crew import Crew
 from crewai.task import Task
@@ -230,3 +232,120 @@ def test_max_usage_count_is_respected():
     crew.kickoff()
     assert tool.max_usage_count == 5
     assert tool.current_usage_count == 5
+
+
+# =============================================================================
+# Schema Validation in run() Tests
+# =============================================================================
+
+
+class CodeExecutorInput(BaseModel):
+    code: str = Field(description="The code to execute")
+    language: str = Field(default="python", description="Programming language")
+
+
+class CodeExecutorTool(BaseTool):
+    name: str = "code_executor"
+    description: str = "Execute code snippets"
+    args_schema: type[BaseModel] = CodeExecutorInput
+
+    def _run(self, code: str, language: str = "python") -> str:
+        return f"Executed {language}: {code}"
+
+
+class TestBaseToolRunValidation:
+    """Tests for args_schema validation in BaseTool.run()."""
+
+    def test_run_with_valid_kwargs_passes_validation(self) -> None:
+        """Valid keyword arguments should pass schema validation and execute."""
+        t = CodeExecutorTool()
+        result = t.run(code="print('hello')")
+        assert result == "Executed python: print('hello')"
+
+    def test_run_with_all_kwargs_passes_validation(self) -> None:
+        """All keyword arguments including optional ones should pass."""
+        t = CodeExecutorTool()
+        result = t.run(code="console.log('hi')", language="javascript")
+        assert result == "Executed javascript: console.log('hi')"
+
+    def test_run_with_missing_required_kwarg_raises(self) -> None:
+        """Missing required kwargs should raise ValueError from schema validation."""
+        t = CodeExecutorTool()
+        with pytest.raises(ValueError, match="validation failed"):
+            t.run(language="python")
+
+    def test_run_with_wrong_field_name_raises(self) -> None:
+        """Kwargs not matching any schema field should trigger validation error
+        for missing required fields."""
+        t = CodeExecutorTool()
+        with pytest.raises(ValueError, match="validation failed"):
+            t.run(wrong_arg="value")
+
+    def test_run_with_positional_args_skips_validation(self) -> None:
+        """Positional-arg calls should bypass schema validation (backwards compat)."""
+        class SimpleTool(BaseTool):
+            name: str = "simple"
+            description: str = "A simple tool"
+
+            def _run(self, question: str) -> str:
+                return question
+
+        t = SimpleTool()
+        result = t.run("What is life?")
+        assert result == "What is life?"
+
+    def test_run_strips_extra_kwargs_from_llm(self) -> None:
+        """Extra kwargs not in the schema should be silently stripped,
+        preventing unexpected-keyword crashes in _run."""
+        t = CodeExecutorTool()
+        result = t.run(code="1+1", extra_hallucinated_field="junk")
+        assert result == "Executed python: 1+1"
+
+    def test_run_increments_usage_after_validation(self) -> None:
+        """Usage count should still increment after validated execution."""
+        t = CodeExecutorTool()
+        assert t.current_usage_count == 0
+        t.run(code="x = 1")
+        assert t.current_usage_count == 1
+
+    def test_run_does_not_increment_usage_on_validation_error(self) -> None:
+        """Usage count should NOT increment when validation fails."""
+        t = CodeExecutorTool()
+        assert t.current_usage_count == 0
+        with pytest.raises(ValueError):
+            t.run(wrong="bad")
+        assert t.current_usage_count == 0
+
+
+class TestToolDecoratorRunValidation:
+    """Tests for args_schema validation in Tool.run() (decorator-based tools)."""
+
+    def test_decorator_tool_run_validates_kwargs(self) -> None:
+        """Decorator-created tools should also validate kwargs against schema."""
+        @tool("execute_code")
+        def execute_code(code: str, language: str = "python") -> str:
+            """Execute a code snippet."""
+            return f"Executed {language}: {code}"
+
+        result = execute_code.run(code="x = 1")
+        assert result == "Executed python: x = 1"
+
+    def test_decorator_tool_run_rejects_missing_required(self) -> None:
+        """Decorator tools should reject missing required args via validation."""
+        @tool("execute_code")
+        def execute_code(code: str) -> str:
+            """Execute a code snippet."""
+            return f"Executed: {code}"
+
+        with pytest.raises(ValueError, match="validation failed"):
+            execute_code.run(wrong_arg="value")
+
+    def test_decorator_tool_positional_args_still_work(self) -> None:
+        """Positional args to decorator tools should bypass validation."""
+        @tool("greet")
+        def greet(name: str) -> str:
+            """Greet someone."""
+            return f"Hello, {name}!"
+
+        result = greet.run("World")
+        assert result == "Hello, World!"