diff --git a/hermes_cli/kanban_db.py b/hermes_cli/kanban_db.py
index 0db694ff5b..9d5ddad6ed 100644
--- a/hermes_cli/kanban_db.py
+++ b/hermes_cli/kanban_db.py
@@ -93,6 +93,7 @@ from toolsets import get_toolset_names
 VALID_STATUSES = {"triage", "todo", "ready", "running", "blocked", "done", "archived"}
 VALID_WORKSPACE_KINDS = {"scratch", "worktree", "dir"}
 KNOWN_TOOLSET_NAMES = frozenset(name.casefold() for name in get_toolset_names())
+_IS_WINDOWS = sys.platform == "win32"
 
 # A running task's claim is valid for 15 minutes; after that the next
 # dispatcher tick reclaims it.  Workers that outlive this window should call
@@ -4024,6 +4025,7 @@ def _default_spawn(
             stderr=subprocess.STDOUT,
             env=env,
             start_new_session=True,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
     except FileNotFoundError:
         log_f.close()
diff --git a/tools/code_execution_tool.py b/tools/code_execution_tool.py
index 3822ce539f..bdbc4bfbe1 100644
--- a/tools/code_execution_tool.py
+++ b/tools/code_execution_tool.py
@@ -1238,6 +1238,7 @@ def execute_code(
             stderr=subprocess.PIPE,
             stdin=subprocess.DEVNULL,
             preexec_fn=None if _IS_WINDOWS else os.setsid,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
 
         # --- Poll loop: watch for exit, timeout, and interrupt ---
@@ -1568,6 +1569,7 @@ def _is_usable_python(python_path: str) -> bool:
              "import sys; sys.exit(0 if sys.version_info >= (3, 8) else 1)"],
             timeout=5,
             capture_output=True,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
         return result.returncode == 0
     except (OSError, subprocess.TimeoutExpired, subprocess.SubprocessError):
diff --git a/tools/environments/local.py b/tools/environments/local.py
index 3b9d65449f..177e5efab1 100644
--- a/tools/environments/local.py
+++ b/tools/environments/local.py
@@ -513,6 +513,7 @@ class LocalEnvironment(BaseEnvironment):
             stderr=subprocess.STDOUT,
             stdin=subprocess.PIPE if stdin_data is not None else subprocess.DEVNULL,
             preexec_fn=None if _IS_WINDOWS else os.setsid,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
             cwd=_popen_cwd,
         )
         if not _IS_WINDOWS:
diff --git a/tools/process_registry.py b/tools/process_registry.py
index 184939adf7..8429a71e08 100644
--- a/tools/process_registry.py
+++ b/tools/process_registry.py
@@ -557,6 +557,7 @@ class ProcessRegistry:
             stderr=subprocess.STDOUT,
             stdin=subprocess.PIPE,
             preexec_fn=None if _IS_WINDOWS else os.setsid,
+            creationflags=subprocess.CREATE_NO_WINDOW if _IS_WINDOWS else 0,
         )
 
         session.process = proc