[BUG] property defaults to type string even if type is defined via anyOf

[wistuba]

Checks

• I have updated to the lastest minor and patch version of Strands
• I have checked the documentation and this is not expected behavior
• I have searched ./issues and there are no duplicates of my issue

Strands Version

latest

Python Version

3.12

Operating System

AL2

Installation Method

pip

Steps to Reproduce

import copy

from strands.tools import normalize_tool_spec


def test_schema():
    schema = {
      "name": "sleep",
      "description": "Pause execution for the specified number of seconds.\n\nThis tool pauses the execution flow for the given number of seconds.\nIt can be interrupted with SIGINT (Ctrl+C).\n\nArgs:\n    seconds (Union[int, float]): Number of seconds to sleep.\n        Must be a positive number greater than 0 and less than or equal to\n        the maximum allowed value (default: 300 seconds, configurable via\n        MAX_SLEEP_SECONDS environment variable).\n\nReturns:\n    str: A message indicating the sleep completed or was interrupted.\n\nRaises:\n    ValueError: If seconds is not positive, exceeds the maximum allowed value,\n               or is not a number.\n\nExamples:\n    >>> sleep(5)  # Sleeps for 5 seconds\n    'Started sleep at 2025-05-30 11:30:00, slept for 5.0 seconds'\n\n    >>> sleep(0.5)  # Sleeps for half a second\n    'Started sleep at 2025-05-30 11:30:00, slept for 0.5 seconds'",
      "inputSchema": {
        "json": {
          "properties": {
            "seconds": {
              "anyOf": [
                {
                  "type": "integer"
                },
                {
                  "type": "number"
                }
              ],
              "description": "Number of seconds to sleep.\nMust be a positive number greater than 0 and less than or equal to\nthe maximum allowed value (default: 300 seconds, configurable via\nMAX_SLEEP_SECONDS environment variable)."
            }
          },
          "required": [
            "seconds"
          ],
          "type": "object"
        }
      }
    }
    assert normalize_tool_spec(copy.deepcopy(schema)) == schema

Expected Behavior

don't add default type "string" in case there is "anyOf". maybe never add it.

Actual Behavior

There is a bug in _normalize_property, in particular:

sdk-python/src/strands/tools/tools.py

Line 91 in 071f89f

normalized_prop.setdefault("type", "string")

pytest output:

                        'equal to\n'
                        'the maximum allowed value (default: 300 seconds, '
                        'configurable via\n'
                        'MAX_SLEEP_SECONDS environment variable).',
+                       'type': 'string',
                    },
                },
                'required': [
                    'seconds',
                ],
                'type': 'object',
            },
        },
        'name': 'sleep',
    }

Additional Context

No response

Possible Solution

No response

Related Issues

No response