diff --git a/src/trading_lab/cli/main.py b/src/trading_lab/cli/main.py
index 442dcdc..750e43d 100644
--- a/src/trading_lab/cli/main.py
+++ b/src/trading_lab/cli/main.py
@@ -10,6 +10,14 @@ def _run(command: list[str]) -> int:
 
 
 def main() -> None:
+    argv_list = __import__("sys").argv[1:]
+    if argv_list and argv_list[0] in {"start", "stop", "service"}:
+        from trading_lab.portfolio import service as _tl_service
+
+        if argv_list[0] == "service":
+            raise SystemExit(_tl_service.main(argv_list[1:] or ["status"]))
+        raise SystemExit(_tl_service.main(argv_list))
+
     parser = argparse.ArgumentParser(prog="tl")
     sub = parser.add_subparsers(dest="command")
 
diff --git a/src/trading_lab/portfolio/gui.py b/src/trading_lab/portfolio/gui.py
index 4f7a279..91fd70d 100644
--- a/src/trading_lab/portfolio/gui.py
+++ b/src/trading_lab/portfolio/gui.py
@@ -9,7 +9,7 @@
 from trading_lab.portfolio.gui_render import render_status_page
 
 
-def run_gui(host: str = "127.0.0.1", port: int = 8765) -> None:
+def run_gui(host: str = "127.0.0.1", port: int = 811, open_browser: bool = True) -> None:
     class Handler(BaseHTTPRequestHandler):
         def do_GET(self) -> None:
             query = parse_qs(self.path.split("?", 1)[1]) if "?" in self.path else {}
@@ -46,7 +46,7 @@ def log_message(self, format: str, *args) -> None:
     url = f"http://{host}:{server.server_port}/"
     print(f"Local-only portfolio GUI: {url}")
     print("Press Ctrl+C to stop.")
-    webbrowser.open(url)
+    webbrowser.open(url) if open_browser else None
     try:
         server.serve_forever()
     except KeyboardInterrupt:
diff --git a/src/trading_lab/portfolio/service.py b/src/trading_lab/portfolio/service.py
new file mode 100644
index 0000000..c71e48c
--- /dev/null
+++ b/src/trading_lab/portfolio/service.py
@@ -0,0 +1,238 @@
+"""Background localhost service for the portfolio GUI.
+
+This module is intentionally local-only:
+- binds to 127.0.0.1
+- stores PID/log files under gitignored data/runtime
+- never talks to a broker
+- never places orders
+"""
+
+from __future__ import annotations
+
+import argparse
+import os
+import platform
+import signal
+import subprocess
+import sys
+import time
+import webbrowser
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Sequence
+from urllib.error import URLError
+from urllib.request import urlopen
+
+
+DEFAULT_HOST = "127.0.0.1"
+DEFAULT_PORT = 811
+RUNTIME_DIR = Path("data/runtime")
+PID_FILE = RUNTIME_DIR / "tl_gui.pid"
+LOG_FILE = RUNTIME_DIR / "tl_gui.log"
+
+
+@dataclass(frozen=True)
+class ServiceStatus:
+    running: bool
+    pid: int | None
+    url: str
+    pid_file: Path
+    log_file: Path
+
+
+def service_url(host: str = DEFAULT_HOST, port: int = DEFAULT_PORT) -> str:
+    return f"http://{host}:{port}/"
+
+
+def _read_pid(pid_file: Path = PID_FILE) -> int | None:
+    try:
+        text = pid_file.read_text(encoding="utf-8").strip()
+    except FileNotFoundError:
+        return None
+    if not text:
+        return None
+    try:
+        return int(text)
+    except ValueError:
+        return None
+
+
+def _pid_is_running(pid: int) -> bool:
+    if pid <= 0:
+        return False
+    try:
+        os.kill(pid, 0)
+    except OSError:
+        return False
+    return True
+
+
+def _server_responds(host: str = DEFAULT_HOST, port: int = DEFAULT_PORT) -> bool:
+    try:
+        with urlopen(service_url(host, port), timeout=1.5) as response:
+            return 200 <= int(response.status) < 500
+    except (OSError, URLError, TimeoutError):
+        return False
+
+
+def status(host: str = DEFAULT_HOST, port: int = DEFAULT_PORT) -> ServiceStatus:
+    pid = _read_pid()
+    running = bool(pid and _pid_is_running(pid)) or _server_responds(host, port)
+    return ServiceStatus(
+        running=running,
+        pid=pid,
+        url=service_url(host, port),
+        pid_file=PID_FILE,
+        log_file=LOG_FILE,
+    )
+
+
+def _creationflags_for_windows() -> int:
+    if platform.system().lower() != "windows":
+        return 0
+    flags = 0
+    for name in ("CREATE_NEW_PROCESS_GROUP", "DETACHED_PROCESS"):
+        flags |= int(getattr(subprocess, name, 0))
+    return flags
+
+
+def _popen_kwargs(log_file):
+    system = platform.system().lower()
+    kwargs: dict[str, object] = {
+        "stdin": subprocess.DEVNULL,
+        "stdout": log_file,
+        "stderr": subprocess.STDOUT,
+        "cwd": str(Path.cwd()),
+    }
+    if system == "windows":
+        kwargs["creationflags"] = _creationflags_for_windows()
+    else:
+        kwargs["start_new_session"] = True
+    return kwargs
+
+
+def start(
+    host: str = DEFAULT_HOST,
+    port: int = DEFAULT_PORT,
+    *,
+    open_browser: bool = True,
+    force: bool = False,
+) -> ServiceStatus:
+    RUNTIME_DIR.mkdir(parents=True, exist_ok=True)
+
+    current = status(host, port)
+    if current.running and not force:
+        if open_browser:
+            webbrowser.open(current.url)
+        return current
+
+    if current.pid and force:
+        stop(host, port)
+
+    LOG_FILE.parent.mkdir(parents=True, exist_ok=True)
+    log_handle = LOG_FILE.open("a", encoding="utf-8")
+
+    cmd = [
+        sys.executable,
+        "-m",
+        "trading_lab.portfolio.service",
+        "serve",
+        "--host",
+        host,
+        "--port",
+        str(port),
+    ]
+
+    process = subprocess.Popen(cmd, **_popen_kwargs(log_handle))
+    PID_FILE.write_text(str(process.pid), encoding="utf-8")
+
+    # Give the server a short moment to bind.
+    for _ in range(25):
+        if _server_responds(host, port):
+            break
+        time.sleep(0.2)
+
+    final = status(host, port)
+    if open_browser:
+        webbrowser.open(final.url)
+    return final
+
+
+def stop(host: str = DEFAULT_HOST, port: int = DEFAULT_PORT) -> ServiceStatus:
+    pid = _read_pid()
+    if pid and _pid_is_running(pid):
+        try:
+            if platform.system().lower() == "windows":
+                subprocess.run(
+                    ["taskkill", "/PID", str(pid), "/T", "/F"],
+                    stdout=subprocess.DEVNULL,
+                    stderr=subprocess.DEVNULL,
+                    check=False,
+                )
+            else:
+                os.kill(pid, signal.SIGTERM)
+        except OSError:
+            pass
+
+    if PID_FILE.exists():
+        PID_FILE.unlink()
+
+    # Give the OS a moment to release the port.
+    time.sleep(0.5)
+    return status(host, port)
+
+
+def serve(host: str = DEFAULT_HOST, port: int = DEFAULT_PORT) -> None:
+    # Import lazily so normal CLI startup stays fast.
+    from trading_lab.portfolio.gui import run_gui
+
+    run_gui(host=host, port=port, open_browser=False)
+
+
+def print_status(state: ServiceStatus) -> None:
+    if state.running:
+        pid_text = str(state.pid) if state.pid else "unknown"
+        print(f"tl GUI service: RUNNING")
+        print(f"URL: {state.url}")
+        print(f"PID: {pid_text}")
+        print(f"Log: {state.log_file}")
+    else:
+        print("tl GUI service: STOPPED")
+        print(f"URL: {state.url}")
+        print(f"PID file: {state.pid_file}")
+        print(f"Log: {state.log_file}")
+
+
+def main(argv: Sequence[str] | None = None) -> int:
+    parser = argparse.ArgumentParser(description="Manage the trading-lab portfolio GUI service.")
+    sub = parser.add_subparsers(dest="cmd", required=True)
+
+    for name in ("start", "stop", "status", "serve"):
+        p = sub.add_parser(name)
+        p.add_argument("--host", default=DEFAULT_HOST)
+        p.add_argument("--port", type=int, default=DEFAULT_PORT)
+
+    sub.choices["start"].add_argument("--no-open", action="store_true")
+    sub.choices["start"].add_argument("--force", action="store_true")
+
+    args = parser.parse_args(argv)
+
+    if args.cmd == "start":
+        print_status(start(args.host, args.port, open_browser=not args.no_open, force=args.force))
+        return 0
+    if args.cmd == "stop":
+        print_status(stop(args.host, args.port))
+        return 0
+    if args.cmd == "status":
+        print_status(status(args.host, args.port))
+        return 0
+    if args.cmd == "serve":
+        serve(args.host, args.port)
+        return 0
+
+    parser.error(f"unknown command {args.cmd}")
+    return 2
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/tests/test_portfolio_service.py b/tests/test_portfolio_service.py
new file mode 100644
index 0000000..a82a833
--- /dev/null
+++ b/tests/test_portfolio_service.py
@@ -0,0 +1,47 @@
+from pathlib import Path
+
+from trading_lab.portfolio import service
+
+
+def test_service_defaults_use_lab_port():
+    assert service.DEFAULT_HOST == "127.0.0.1"
+    assert service.DEFAULT_PORT == 811
+    assert service.service_url() == "http://127.0.0.1:811/"
+
+
+def test_service_status_handles_missing_pid_file(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.setattr(service, "RUNTIME_DIR", Path("data/runtime"))
+    monkeypatch.setattr(service, "PID_FILE", Path("data/runtime/tl_gui.pid"))
+    monkeypatch.setattr(service, "LOG_FILE", Path("data/runtime/tl_gui.log"))
+    monkeypatch.setattr(service, "_server_responds", lambda host, port: False)
+
+    state = service.status()
+    assert state.running is False
+    assert state.pid is None
+    assert str(state.url).endswith(":811/")
+
+
+def test_service_stop_removes_pid_file_without_real_process(tmp_path, monkeypatch):
+    monkeypatch.chdir(tmp_path)
+    runtime = Path("data/runtime")
+    runtime.mkdir(parents=True)
+    pid_file = runtime / "tl_gui.pid"
+    pid_file.write_text("999999", encoding="utf-8")
+
+    monkeypatch.setattr(service, "RUNTIME_DIR", runtime)
+    monkeypatch.setattr(service, "PID_FILE", pid_file)
+    monkeypatch.setattr(service, "LOG_FILE", runtime / "tl_gui.log")
+    monkeypatch.setattr(service, "_pid_is_running", lambda pid: False)
+    monkeypatch.setattr(service, "_server_responds", lambda host, port: False)
+
+    state = service.stop()
+    assert state.running is False
+    assert not pid_file.exists()
+
+
+def test_cli_has_top_level_service_shortcuts():
+    import trading_lab.cli.main as cli_main
+
+    text = Path(cli_main.__file__).read_text(encoding="utf-8")
+    assert '"start", "stop", "service"' in text