feat: add public tool_spec setter

src/strands/tools/decorator.py

@@ -541,6 +541,31 @@ def tool_spec(self) -> ToolSpec:
         """
         return self._tool_spec
 
+    @tool_spec.setter
+    def tool_spec(self, value: ToolSpec) -> None:
+        """Set the tool specification.
+
+        This allows runtime modification of the tool's schema, enabling dynamic
+        tool configurations based on feature flags or other runtime conditions.
+
+        Args:
+            value: The new tool specification.
+
+        Raises:
+            ValueError: If the spec fails structural validation (wrong name or
+                missing required field).
+        """
+        if value.get("name") != self._tool_name:
+            raise ValueError(
+                f"cannot change tool name via tool_spec (expected '{self._tool_name}', got '{value.get('name')}')"
+            )
+
+        for field in ("description", "inputSchema"):
+            if field not in value:
+                raise ValueError(f"tool_spec must contain '{field}'")
+
+        self._tool_spec = value
+
     @property
     def tool_type(self) -> str:
         """Get the type of the tool.

src/strands/tools/tools.py

@@ -197,6 +197,31 @@ def tool_spec(self) -> ToolSpec:
         """
         return self._tool_spec
 
+    @tool_spec.setter
+    def tool_spec(self, value: ToolSpec) -> None:
+        """Set the tool specification.
+
+        This allows runtime modification of the tool's schema, enabling dynamic
+        tool configurations based on feature flags or other runtime conditions.
+
+        Args:
+            value: The new tool specification.
+
+        Raises:
+            ValueError: If the spec fails structural validation (wrong name or
+                missing required field).
+        """
+        if value.get("name") != self._tool_name:
+            raise ValueError(
+                f"cannot change tool name via tool_spec (expected '{self._tool_name}', got '{value.get('name')}')"
+            )
+
+        for field in ("description", "inputSchema"):
+            if field not in value:
+                raise ValueError(f"tool_spec must contain '{field}'")
+
+        self._tool_spec = value
+
     @property
     def supports_hot_reload(self) -> bool:
         """Check if this tool supports automatic reloading when modified.

tests/strands/tools/test_tool_spec_setter.py

@@ -0,0 +1,253 @@
+"""Tests for tool_spec setter on DecoratedFunctionTool and PythonAgentTool."""
+
+import pytest
+
+from strands.tools.decorator import tool
+from strands.tools.tools import PythonAgentTool
+from strands.types.tools import ToolSpec
+
+
+class TestDecoratedFunctionToolSpecSetter:
+    """Tests for DecoratedFunctionTool.tool_spec setter."""
+
+    def test_set_tool_spec_replaces_spec(self):
+        @tool
+        def my_tool(query: str) -> str:
+            """A test tool."""
+            return query
+
+        new_spec: ToolSpec = {
+            "name": "my_tool",
+            "description": "Updated tool",
+            "inputSchema": {
+                "json": {
+                    "type": "object",
+                    "properties": {
+                        "query": {"type": "string", "description": "The query"},
+                        "limit": {"type": "integer", "description": "Max results"},
+                    },
+                    "required": ["query"],
+                }
+            },
+        }
+        my_tool.tool_spec = new_spec
+        assert my_tool.tool_spec is new_spec
+        assert "limit" in my_tool.tool_spec["inputSchema"]["json"]["properties"]
+
+    def test_set_tool_spec_persists_across_reads(self):
+        @tool
+        def another_tool(x: int) -> int:
+            """Another test tool."""
+            return x
+
+        new_spec: ToolSpec = {
+            "name": "another_tool",
+            "description": "Modified",
+            "inputSchema": {
+                "json": {
+                    "type": "object",
+                    "properties": {"x": {"type": "integer"}, "y": {"type": "integer"}},
+                    "required": ["x"],
+                }
+            },
+        }
+        another_tool.tool_spec = new_spec
+        assert another_tool.tool_spec["description"] == "Modified"
+        assert another_tool.tool_spec["description"] == "Modified"
+
+    def test_add_property_via_setter(self):
+        @tool
+        def dynamic_tool(base: str) -> str:
+            """A dynamic tool."""
+            return base
+
+        spec = dynamic_tool.tool_spec.copy()
+        spec["inputSchema"] = dynamic_tool.tool_spec["inputSchema"].copy()
+        spec["inputSchema"]["json"] = dynamic_tool.tool_spec["inputSchema"]["json"].copy()
+        spec["inputSchema"]["json"]["properties"] = dynamic_tool.tool_spec["inputSchema"]["json"]["properties"].copy()
+        spec["inputSchema"]["json"]["properties"]["extra"] = {
+            "type": "string",
+            "description": "Extra param",
+        }
+        dynamic_tool.tool_spec = spec
+        assert "extra" in dynamic_tool.tool_spec["inputSchema"]["json"]["properties"]
+
+    def test_set_tool_spec_rejects_name_change(self):
+        @tool
+        def my_tool(query: str) -> str:
+            """A test tool."""
+            return query
+
+        bad_spec: ToolSpec = {
+            "name": "wrong_name",
+            "description": "Updated tool",
+            "inputSchema": {"json": {"type": "object", "properties": {}, "required": []}},
+        }
+        with pytest.raises(ValueError, match="cannot change tool name via tool_spec"):
+            my_tool.tool_spec = bad_spec
+
+    def test_set_tool_spec_rejects_missing_description(self):
+        @tool
+        def my_tool(query: str) -> str:
+            """A test tool."""
+            return query
+
+        bad_spec: ToolSpec = {
+            "name": "my_tool",
+            "inputSchema": {"json": {"type": "object", "properties": {}, "required": []}},
+        }
+        with pytest.raises(ValueError, match="tool_spec must contain 'description'"):
+            my_tool.tool_spec = bad_spec
+
+    def test_set_tool_spec_rejects_missing_input_schema(self):
+        @tool
+        def my_tool(query: str) -> str:
+            """A test tool."""
+            return query
+
+        bad_spec: ToolSpec = {
+            "name": "my_tool",
+            "description": "Updated tool",
+        }
+        with pytest.raises(ValueError, match="tool_spec must contain 'inputSchema'"):
+            my_tool.tool_spec = bad_spec
+
+    def test_set_tool_spec_accepts_bare_input_schema(self):
+        @tool
+        def my_tool(query: str) -> str:
+            """A test tool."""
+            return query
+
+        bare_spec: ToolSpec = {
+            "name": "my_tool",
+            "description": "Bare schema",
+            "inputSchema": {"type": "object", "properties": {"query": {"type": "string"}}, "required": ["query"]},
+        }
+        my_tool.tool_spec = bare_spec
+        assert my_tool.tool_spec is bare_spec
+
+    def test_set_tool_spec_accepts_valid_spec(self):
+        @tool
+        def my_tool(query: str) -> str:
+            """A test tool."""
+            return query
+
+        valid_spec: ToolSpec = {
+            "name": "my_tool",
+            "description": "A valid updated spec",
+            "inputSchema": {
+                "json": {
+                    "type": "object",
+                    "properties": {"query": {"type": "string"}},
+                    "required": ["query"],
+                }
+            },
+        }
+        my_tool.tool_spec = valid_spec
+        assert my_tool.tool_spec is valid_spec
+
+
+class TestPythonAgentToolSpecSetter:
+    """Tests for PythonAgentTool.tool_spec setter."""
+
+    def _make_tool(self) -> PythonAgentTool:
+        def func(tool_use, **kwargs):
+            return {"status": "success", "content": [{"text": "ok"}], "toolUseId": tool_use["toolUseId"]}
+
+        spec: ToolSpec = {
+            "name": "test_tool",
+            "description": "A test tool",
+            "inputSchema": {
+                "json": {
+                    "type": "object",
+                    "properties": {"input": {"type": "string"}},
+                    "required": ["input"],
+                }
+            },
+        }
+        return PythonAgentTool("test_tool", spec, func)
+
+    def test_set_tool_spec(self):
+        t = self._make_tool()
+        new_spec: ToolSpec = {
+            "name": "test_tool",
+            "description": "Updated",
+            "inputSchema": {
+                "json": {
+                    "type": "object",
+                    "properties": {
+                        "input": {"type": "string"},
+                        "extra": {"type": "integer"},
+                    },
+                    "required": ["input"],
+                }
+            },
+        }
+        t.tool_spec = new_spec
+        assert t.tool_spec is new_spec
+        assert "extra" in t.tool_spec["inputSchema"]["json"]["properties"]
+
+    def test_set_tool_spec_persists(self):
+        t = self._make_tool()
+        new_spec: ToolSpec = {
+            "name": "test_tool",
+            "description": "Persisted",
+            "inputSchema": {"json": {"type": "object", "properties": {}, "required": []}},
+        }
+        t.tool_spec = new_spec
+        assert t.tool_spec["description"] == "Persisted"
+        assert t.tool_spec["description"] == "Persisted"
+
+    def test_set_tool_spec_rejects_name_change(self):
+        t = self._make_tool()
+        bad_spec: ToolSpec = {
+            "name": "wrong_name",
+            "description": "Updated",
+            "inputSchema": {"json": {"type": "object", "properties": {}, "required": []}},
+        }
+        with pytest.raises(ValueError, match="cannot change tool name via tool_spec"):
+            t.tool_spec = bad_spec
+
+    def test_set_tool_spec_rejects_missing_description(self):
+        t = self._make_tool()
+        bad_spec: ToolSpec = {
+            "name": "test_tool",
+            "inputSchema": {"json": {"type": "object", "properties": {}, "required": []}},
+        }
+        with pytest.raises(ValueError, match="tool_spec must contain 'description'"):
+            t.tool_spec = bad_spec
+
+    def test_set_tool_spec_rejects_missing_input_schema(self):
+        t = self._make_tool()
+        bad_spec: ToolSpec = {
+            "name": "test_tool",
+            "description": "Updated",
+        }
+        with pytest.raises(ValueError, match="tool_spec must contain 'inputSchema'"):
+            t.tool_spec = bad_spec
+
+    def test_set_tool_spec_accepts_bare_input_schema(self):
+        t = self._make_tool()
+        bare_spec: ToolSpec = {
+            "name": "test_tool",
+            "description": "Bare schema",
+            "inputSchema": {"type": "object", "properties": {"input": {"type": "string"}}, "required": ["input"]},
+        }
+        t.tool_spec = bare_spec
+        assert t.tool_spec is bare_spec
+
+    def test_set_tool_spec_accepts_valid_spec(self):
+        t = self._make_tool()
+        valid_spec: ToolSpec = {
+            "name": "test_tool",
+            "description": "A valid updated spec",
+            "inputSchema": {
+                "json": {
+                    "type": "object",
+                    "properties": {"input": {"type": "string"}},
+                    "required": ["input"],
+                }
+            },
+        }
+        t.tool_spec = valid_spec
+        assert t.tool_spec is valid_spec