diff --git a/src/workflow/CommandExecutor.py b/src/workflow/CommandExecutor.py
index 86f265b2..2aeb088c 100644
--- a/src/workflow/CommandExecutor.py
+++ b/src/workflow/CommandExecutor.py
@@ -284,6 +284,12 @@ def run_topp(self, tool: str, input_output: dict, custom_params: dict = {}) -> b
             # Add non-default TOPP tool parameters
             if tool in params.keys():
                 for k, v in params[tool].items():
+                    # Boolean flag handling (from registerFlag_ params):
+                    # True -> emit flag only, False -> skip entirely
+                    if isinstance(v, bool):
+                        if v:
+                            command += [f"-{k}"]
+                        continue
                     command += [f"-{k}"]
                     # Skip only empty strings (pass flag with no value)
                     # Note: 0 and 0.0 are valid values, so use explicit check
diff --git a/tests/test_boolean_flag_params.py b/tests/test_boolean_flag_params.py
new file mode 100644
index 00000000..147c55aa
--- /dev/null
+++ b/tests/test_boolean_flag_params.py
@@ -0,0 +1,173 @@
+"""
+Tests for boolean flag parameter handling in CommandExecutor.run_topp().
+
+Verifies that:
+- Python bool True (flag-style) emits only the flag, no value
+- Python bool False (flag-style) omits the flag entirely
+- String "true"/"false" (string-style) emits -param true / -param false
+- Other parameter types (int, float, str, empty, multiline) are unchanged
+"""
+import os
+import sys
+import json
+import pytest
+from pathlib import Path
+from unittest.mock import patch, MagicMock
+
+# Add project root to path
+PROJECT_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+sys.path.append(PROJECT_ROOT)
+
+# Mock pyopenms and streamlit before importing project modules
+mock_pyopenms = MagicMock()
+mock_pyopenms.__version__ = "3.0.0"
+sys.modules['pyopenms'] = mock_pyopenms
+
+mock_streamlit = MagicMock()
+mock_streamlit.session_state = {"settings": {"max_threads": {"local": 4, "online": 2}}}
+sys.modules['streamlit'] = mock_streamlit
+
+from src.workflow.ParameterManager import ParameterManager
+from src.workflow.CommandExecutor import CommandExecutor
+from src.workflow.Logger import Logger
+
+
+@pytest.fixture
+def workflow_env(tmp_path):
+    """
+    Set up a realistic workflow environment with a fake ini file and params.json.
+
+    Creates:
+    - tmp_path/ini/FakeTool.ini (empty file, run_topp only checks existence)
+    - tmp_path/params.json with mixed parameter types
+    """
+    # Create ini directory and fake ini file
+    ini_dir = tmp_path / "ini"
+    ini_dir.mkdir()
+    ini_file = ini_dir / "FakeTool.ini"
+    ini_file.write_text("<PARAMETERS></PARAMETERS>")
+
+    # Write params.json with all parameter type variants
+    params = {
+        "FakeTool": {
+            "enable_feature": True,         # bool True -> flag only
+            "disable_feature": False,        # bool False -> omit entirely
+            "string_bool_on": "true",        # str "true" -> -param true
+            "string_bool_off": "false",      # str "false" -> -param false
+            "threshold": 1000.0,             # float
+            "mode": "fast",                  # regular string
+            "count": 5,                      # int
+            "empty_flag": "",                # empty string -> flag only
+            "multi_value": "val1\nval2",     # multiline string -> split
+        }
+    }
+    params_file = tmp_path / "params.json"
+    params_file.write_text(json.dumps(params, indent=4))
+
+    return tmp_path
+
+
+@pytest.fixture
+def captured_command(workflow_env):
+    """
+    Create a CommandExecutor with mocked dependencies, call run_topp(),
+    and return the command list that would have been executed.
+    """
+    captured = {}
+
+    pm = ParameterManager(workflow_env)
+    logger = MagicMock(spec=Logger)
+    executor = CommandExecutor(workflow_env, logger, pm)
+
+    # Capture the command instead of executing it
+    def fake_run_command(cmd):
+        captured["command"] = cmd
+        return True
+
+    executor.run_command = fake_run_command
+
+    executor.run_topp("FakeTool", {"in": ["input.mzML"]})
+
+    return captured["command"]
+
+
+class TestBooleanFlagParams:
+    """Test boolean flag parameter handling in run_topp()."""
+
+    def test_bool_true_emits_flag_only(self, captured_command):
+        """Python bool True should emit -flag with no following value."""
+        idx = captured_command.index("-enable_feature")
+        # Next element should NOT be "True" — it should be another flag or -threads
+        next_elem = captured_command[idx + 1]
+        assert next_elem.startswith("-"), (
+            f"Expected flag-only for bool True, but got value '{next_elem}' after -enable_feature"
+        )
+
+    def test_bool_false_omits_flag(self, captured_command):
+        """Python bool False should omit the flag entirely."""
+        assert "-disable_feature" not in captured_command, (
+            "bool False parameter should not appear in command at all"
+        )
+
+    def test_string_true_emits_value(self, captured_command):
+        """String 'true' should emit -param true (with explicit value)."""
+        idx = captured_command.index("-string_bool_on")
+        assert captured_command[idx + 1] == "true", (
+            f"Expected 'true' value after -string_bool_on, got '{captured_command[idx + 1]}'"
+        )
+
+    def test_string_false_emits_value(self, captured_command):
+        """String 'false' should emit -param false (with explicit value)."""
+        idx = captured_command.index("-string_bool_off")
+        assert captured_command[idx + 1] == "false", (
+            f"Expected 'false' value after -string_bool_off, got '{captured_command[idx + 1]}'"
+        )
+
+    def test_float_param(self, captured_command):
+        """Float values should be emitted as string representation."""
+        idx = captured_command.index("-threshold")
+        assert captured_command[idx + 1] == "1000.0"
+
+    def test_string_param(self, captured_command):
+        """Regular string values should be emitted as-is."""
+        idx = captured_command.index("-mode")
+        assert captured_command[idx + 1] == "fast"
+
+    def test_int_param(self, captured_command):
+        """Integer values should be emitted as string representation."""
+        idx = captured_command.index("-count")
+        assert captured_command[idx + 1] == "5"
+
+    def test_empty_string_emits_flag_only(self, captured_command):
+        """Empty string should emit the flag with no value."""
+        idx = captured_command.index("-empty_flag")
+        next_elem = captured_command[idx + 1]
+        assert next_elem.startswith("-"), (
+            f"Expected flag-only for empty string, but got value '{next_elem}'"
+        )
+
+    def test_multiline_string_splits(self, captured_command):
+        """Multiline string should be split into separate values."""
+        idx = captured_command.index("-multi_value")
+        assert captured_command[idx + 1] == "val1"
+        assert captured_command[idx + 2] == "val2"
+
+    def test_threads_present(self, captured_command):
+        """The -threads flag should always be present."""
+        assert "-threads" in captured_command
+
+    def test_ini_flag_present(self, captured_command):
+        """The -ini flag should be present when ini file exists."""
+        assert "-ini" in captured_command
+        idx = captured_command.index("-ini")
+        assert captured_command[idx + 1].endswith("FakeTool.ini")
+
+    def test_input_file_present(self, captured_command):
+        """Input files should be present in the command."""
+        assert "-in" in captured_command
+        idx = captured_command.index("-in")
+        assert captured_command[idx + 1] == "input.mzML"
+
+    def test_command_starts_with_tool(self, captured_command):
+        """Command should start with the tool name."""
+        assert captured_command[0] == "FakeTool"