fix: Allow tool names that start with numbers (#407)

Some MCP servers return tool names that have numeric identifiers that start with a number; open up our regex to allow those names.

This will not allow direct method invocations of those tools, but we can revisit the need for that in the future if it become a concern.

Author: zastrowm

src/strands/tools/tools.py

@@ -48,7 +48,7 @@ def validate_tool_use_name(tool: ToolUse) -> None:
         raise InvalidToolUseNameException(message)
 
     tool_name = tool["name"]
-    tool_name_pattern = r"^[a-zA-Z][a-zA-Z0-9_\-]*$"
+    tool_name_pattern = r"^[a-zA-Z0-9_\-]{1,}$"
     tool_name_max_length = 64
     valid_name_pattern = bool(re.match(tool_name_pattern, tool_name))
     tool_name_len = len(tool_name)

tests/strands/tools/test_tools.py

@@ -59,6 +59,10 @@ def test_validate_tool_use_name_valid():
     # Should not raise an exception
     validate_tool_use_name(tool2)
 
+    tool3 = {"name": "34234_numbers", "toolUseId": "123"}
+    # Should not raise an exception
+    validate_tool_use_name(tool3)
+
 
 def test_validate_tool_use_name_missing():
     tool = {"toolUseId": "123"}
@@ -67,7 +71,7 @@ def test_validate_tool_use_name_missing():
 
 
 def test_validate_tool_use_name_invalid_pattern():
-    tool = {"name": "123_invalid", "toolUseId": "123"}
+    tool = {"name": "+123_invalid", "toolUseId": "123"}
     with pytest.raises(InvalidToolUseNameException, match="invalid tool name pattern"):
         validate_tool_use_name(tool)
 
@@ -414,7 +418,7 @@ def test_validate_tool_use_with_valid_input():
         # Name - Invalid characters
         (
             {
-                "name": "1-invalid",
+                "name": "+1-invalid",
                 "toolUseId": "123",
                 "input": {},
             },
@@ -429,6 +433,15 @@ def test_validate_tool_use_with_valid_input():
             },
             strands.tools.InvalidToolUseNameException,
         ),
+        # Name - Empty
+        (
+            {
+                "name": "",
+                "toolUseId": "123",
+                "input": {},
+            },
+            strands.tools.InvalidToolUseNameException,
+        ),
     ],
 )
 def test_validate_tool_use_invalid(tool_use, expected_error):