fix: allowed_tools=[] treated as falsy instead of disabling all tools

src/claude_agent_sdk/_internal/transport/subprocess_cli.py

@@ -198,7 +198,7 @@ def _build_command(self) -> list[str]:
                 # Preset object - 'claude_code' preset maps to 'default'
                 cmd.extend(["--tools", "default"])
 
-        if self._options.allowed_tools:
+        if self._options.allowed_tools is not None:
             cmd.extend(["--allowedTools", ",".join(self._options.allowed_tools)])
 
         if self._options.max_turns:

src/claude_agent_sdk/types.py

@@ -618,7 +618,7 @@ class ClaudeAgentOptions:
     """Query options for Claude SDK."""
 
     tools: list[str] | ToolsPreset | None = None
-    allowed_tools: list[str] = field(default_factory=list)
+    allowed_tools: list[str] | None = None
     system_prompt: str | SystemPromptPreset | None = None
     mcp_servers: dict[str, McpServerConfig] | str | Path = field(default_factory=dict)
     permission_mode: PermissionMode | None = None

tests/test_transport.py

@@ -684,6 +684,26 @@ def test_build_command_with_tools_preset(self):
         tools_idx = cmd.index("--tools")
         assert cmd[tools_idx + 1] == "default"
 
+    def test_build_command_with_allowed_tools_empty_array(self):
+        """Test that allowed_tools=[] passes --allowedTools with empty value."""
+        transport = SubprocessCLITransport(
+            prompt="test",
+            options=make_options(allowed_tools=[]),
+        )
+        cmd = transport._build_command()
+        assert "--allowedTools" in cmd
+        allowed_idx = cmd.index("--allowedTools")
+        assert cmd[allowed_idx + 1] == ""
+
+    def test_build_command_without_allowed_tools(self):
+        """Test that allowed_tools=None (default) omits --allowedTools."""
+        transport = SubprocessCLITransport(
+            prompt="test",
+            options=make_options(),
+        )
+        cmd = transport._build_command()
+        assert "--allowedTools" not in cmd
+
     def test_build_command_without_tools(self):
         """Test building CLI command without tools option (default None)."""
         transport = SubprocessCLITransport(

tests/test_types.py

@@ -79,7 +79,7 @@ class TestOptions:
     def test_default_options(self):
         """Test Options with default values."""
         options = ClaudeAgentOptions()
-        assert options.allowed_tools == []
+        assert options.allowed_tools is None
         assert options.system_prompt is None
         assert options.permission_mode is None
         assert options.continue_conversation is False