diff --git a/aisuite/client.py b/aisuite/client.py
index 1c46c002..fa3e2958 100644
--- a/aisuite/client.py
+++ b/aisuite/client.py
@@ -17,6 +17,14 @@
 except ImportError:
     MCP_AVAILABLE = False
 
+    # Define a fallback is_mcp_config when MCP is not installed
+    # This allows checking for MCP configs to provide helpful error messages
+    def is_mcp_config(obj: Any) -> bool:
+        """Check if an object looks like an MCP config dict."""
+        if not isinstance(obj, dict):
+            return False
+        return obj.get("type") == "mcp" and "name" in obj
+
 
 class Client:
     def __init__(
diff --git a/tests/client/test_mcp_fallback.py b/tests/client/test_mcp_fallback.py
new file mode 100644
index 00000000..348c1416
--- /dev/null
+++ b/tests/client/test_mcp_fallback.py
@@ -0,0 +1,107 @@
+"""
+Tests for MCP fallback behavior when MCP package is not installed.
+
+This tests the fix for the NameError that occurred when using tools
+without the MCP package installed.
+"""
+
+import pytest
+from unittest.mock import Mock, patch
+
+
+class TestMCPFallback:
+    """Test MCP fallback behavior when MCP is not available."""
+
+    def test_is_mcp_config_fallback_exists(self):
+        """
+        Test that is_mcp_config is always defined, even without MCP.
+        
+        This is a regression test for the bug where using tools without
+        MCP installed would raise: NameError: name 'is_mcp_config' is not defined
+        """
+        # Import the client module - is_mcp_config should always be defined
+        from aisuite import client as client_module
+        
+        # Verify is_mcp_config exists (either from MCP or fallback)
+        assert hasattr(client_module, 'is_mcp_config') or client_module.MCP_AVAILABLE
+        
+    def test_mcp_config_detection(self):
+        """Test that MCP configs are correctly detected."""
+        # Import after any patching
+        from aisuite.client import MCP_AVAILABLE
+        
+        # We need to test the fallback function directly
+        # Define the same logic as the fallback
+        def is_mcp_config_fallback(obj):
+            if not isinstance(obj, dict):
+                return False
+            return obj.get("type") == "mcp" and "name" in obj
+        
+        # Test MCP config detection
+        mcp_config = {"type": "mcp", "name": "test", "command": "npx"}
+        assert is_mcp_config_fallback(mcp_config) == True
+        
+        # Test non-MCP configs
+        function_tool = {"type": "function", "function": {"name": "test"}}
+        assert is_mcp_config_fallback(function_tool) == False
+        
+        # Test non-dict inputs
+        assert is_mcp_config_fallback("not a dict") == False
+        assert is_mcp_config_fallback(None) == False
+
+
+class TestIsMCPConfigFallback:
+    """Direct tests for the is_mcp_config fallback function logic."""
+
+    def test_valid_mcp_config(self):
+        """Test detection of valid MCP configs."""
+        # Inline the fallback logic for testing
+        def is_mcp_config(obj):
+            if not isinstance(obj, dict):
+                return False
+            return obj.get("type") == "mcp" and "name" in obj
+        
+        valid_configs = [
+            {"type": "mcp", "name": "filesystem"},
+            {"type": "mcp", "name": "test", "command": "npx", "args": ["arg1"]},
+            {"type": "mcp", "name": "server", "extra": "data"},
+        ]
+        
+        for config in valid_configs:
+            assert is_mcp_config(config) == True, f"Should detect {config} as MCP config"
+
+    def test_invalid_mcp_config(self):
+        """Test that non-MCP configs are not detected as MCP."""
+        def is_mcp_config(obj):
+            if not isinstance(obj, dict):
+                return False
+            return obj.get("type") == "mcp" and "name" in obj
+        
+        invalid_configs = [
+            {"type": "function", "function": {}},  # OpenAI function format
+            {"name": "test"},  # Missing type
+            {"type": "mcp"},  # Missing name
+            {"type": "other", "name": "test"},  # Wrong type
+            {},  # Empty dict
+        ]
+        
+        for config in invalid_configs:
+            assert is_mcp_config(config) == False, f"Should not detect {config} as MCP config"
+
+    def test_non_dict_inputs(self):
+        """Test that non-dict inputs return False."""
+        def is_mcp_config(obj):
+            if not isinstance(obj, dict):
+                return False
+            return obj.get("type") == "mcp" and "name" in obj
+        
+        non_dicts = [
+            "string",
+            123,
+            12.34,
+            None,
+            [],
+        ]
+        
+        for item in non_dicts:
+            assert is_mcp_config(item) == False, f"Should return False for {type(item)}"