diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..8022c72
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+workspace/settings.json
+workspace/presets.json
+workspace/patterns/*
+!workspace/patterns/__init__.py
+!workspace/patterns/.gitkeep
diff --git a/README.md b/README.md
index 5739f11..055a6a7 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,48 @@
 # led-simulator
 
+Graphical **NeoPixel** simulator for host Python. It uses the same layout as device flash:
+
+- **`led-driver/src`** → flash root **`/`** (application modules, `patterns/`, `presets.json`, …)
+- **`led-driver/lib`** → **`/lib`** (Microdot, utemplate, …)
+
+It runs the **whole application**: **`led-driver/src/main.py`** as **`__main__`** (`runpy.run_path(..., run_name="__main__")` → `asyncio.run(main(port=…))`). Startup matches the device — **`Settings`**, **`presets.load`**, **default preset** from settings, **`patterns/`**, **Microdot** **`/ws`**, **`presets_loop`**, **UDP hello**. Only **`machine`**, **`neopixel`**, **`network`**, **`utime`**, and **`ubinascii`** are stubbed (`stubs/`).
+
+The GUI sets **`LED_SIM_ROOT`** so **`main.py`** can register the Microdot app for **Stop**, and **`LED_SIM_PORT`** for the HTTP/WebSocket listen port (default **80** on device when unset). On the ESP32 those variables are unset.
+
+## Requirements
+
+- Python 3.10+
+- Tk (e.g. `python3-tk` on Debian/Ubuntu if the window fails to open)
+
+## Run
+
+From the repository root:
+
+```bash
+pipenv install   # optional; Microdot is vendored under led-driver/lib
+python3 led-simulator/gui_main.py
+```
+
+## UI
+
+- **Start** / **Stop**: start or stop the full **`main.py`** process (same code path as the chip).
+- **HTTP / WS port**: Microdot listen port; WebSocket URL **`ws://127.0.0.1:<port>/ws`** (JSON **v1**).
+
+Configure the app like on flash: **`workspace/settings.json`** (patched as device settings path), **`presets.json`** and **`patterns/`** under **`led-simulator/workspace/`** when the simulator creates symlinks from **`src/`**, or edit files directly under **`led-driver/src/`** if you use a real **`patterns/`** directory there.
+
+Example pattern modules: **`led-simulator/examples/`** (`Blink`, `Chase`). Copy into **`patterns/`** as on the device.
+
+## Notes
+
+- Changing the port spinbox only takes effect on the next **Start**.
+- If **`led-driver/src/patterns`** already exists as a normal directory, the simulator leaves it in place.
+
+## Shell (no GUI)
+
+```bash
+cd led-driver/src
+PYTHONPATH="../lib:../../led-simulator/stubs" LED_SIM_ROOT="../../led-simulator" LED_SIM_PORT=8765 \
+  python3 main.py
+```
+
+(Adjust paths from your checkout root; **`LED_SIM_ROOT`** must point at **`led-simulator/`** so **Stop**-style hooks work if you use them.)
diff --git a/__pycache__/led_driver_sim_hook.cpython-313.pyc b/__pycache__/led_driver_sim_hook.cpython-313.pyc
new file mode 100644
index 0000000..9b7d425
Binary files /dev/null and b/__pycache__/led_driver_sim_hook.cpython-313.pyc differ
diff --git a/examples/blink.py b/examples/blink.py
new file mode 100644
index 0000000..2ee3734
--- /dev/null
+++ b/examples/blink.py
@@ -0,0 +1,19 @@
+"""Example pattern for led-simulator / led-driver (generator + yield per tick)."""
+
+import utime
+
+
+class Blink:
+    def __init__(self, presets):
+        self.presets = presets
+
+    def run(self, preset):
+        colors = preset.c if preset.c else [(255, 255, 255)]
+        idx = 0
+        delay_ms = max(1, int(preset.d))
+        while True:
+            rgb = colors[idx % len(colors)]
+            self.presets.fill(self.presets.apply_brightness(rgb, preset.b))
+            yield
+            utime.sleep_ms(delay_ms)
+            idx += 1
diff --git a/examples/chase.py b/examples/chase.py
new file mode 100644
index 0000000..baf222f
--- /dev/null
+++ b/examples/chase.py
@@ -0,0 +1,25 @@
+"""Simple one-pixel chase (uses preset c[0] for the dot, preset n3 as step)."""
+
+import utime
+
+
+class Chase:
+    def __init__(self, presets):
+        self.presets = presets
+
+    def run(self, preset):
+        n = self.presets.num_leds
+        rgb = preset.c[0] if preset.c else (255, 64, 0)
+        raw_step = int(getattr(preset, "n3", 1))
+        step = raw_step if raw_step != 0 else 1
+        pos = 0
+        delay_ms = max(1, int(preset.d))
+        while True:
+            off = (0, 0, 0)
+            for i in range(n):
+                self.presets.n[i] = off
+            self.presets.n[pos % n] = self.presets.apply_brightness(rgb, preset.b)
+            self.presets.n.write()
+            yield
+            utime.sleep_ms(delay_ms)
+            pos += step
diff --git a/gui_main.py b/gui_main.py
new file mode 100644
index 0000000..b6ff8ce
--- /dev/null
+++ b/gui_main.py
@@ -0,0 +1,265 @@
+#!/usr/bin/env python3
+"""
+Graphical NeoPixel simulator for led-driver (CPython).
+
+Treats ``led-driver/src`` as flash root (``/``) and ``led-driver/lib`` as ``/lib``.
+**Start** runs the full application: ``led-driver/src/main.py`` as ``__main__``
+(``asyncio.run(main(port=…))``) — same startup as the device: ``settings``,
+``presets.json``, default preset, ``patterns/``, WebSocket, UDP hello, etc.
+"""
+
+from __future__ import annotations
+
+import os
+import queue
+import runpy
+import shutil
+import sys
+import threading
+import tkinter as tk
+from pathlib import Path
+from tkinter import messagebox, ttk
+
+# --- Paths (before importing driver code) ---
+SIM_ROOT = Path(__file__).resolve().parent
+WORKSPACE = SIM_ROOT / "workspace"
+STUBS_ROOT = SIM_ROOT / "stubs"
+DRIVER_ROOT = SIM_ROOT.parent / "led-driver"
+DRIVER_SRC = DRIVER_ROOT / "src"
+DRIVER_LIB = DRIVER_ROOT / "lib"
+DRIVER_MAIN = DRIVER_SRC / "main.py"
+DEFAULT_SETTINGS = SIM_ROOT / "settings.default.json"
+
+
+def _ensure_workspace_dirs():
+    WORKSPACE.mkdir(parents=True, exist_ok=True)
+    (WORKSPACE / "patterns").mkdir(parents=True, exist_ok=True)
+    settings_path = WORKSPACE / "settings.json"
+    if not settings_path.is_file() and DEFAULT_SETTINGS.is_file():
+        shutil.copy2(DEFAULT_SETTINGS, settings_path)
+    presets_path = WORKSPACE / "presets.json"
+    if not presets_path.is_file():
+        presets_path.write_text("{}\n", encoding="utf-8")
+
+
+def _install_driver_path_and_stubs():
+    """``/lib`` then ``/`` then stubs (MicroPython search order, stubs win)."""
+    for p in (DRIVER_LIB, DRIVER_SRC, STUBS_ROOT):
+        sys.path.insert(0, str(p))
+
+
+def _patch_settings_path():
+    _ensure_workspace_dirs()
+    import settings as led_settings
+
+    led_settings.Settings.SETTINGS_FILE = str(WORKSPACE / "settings.json")
+
+
+_install_driver_path_and_stubs()
+_patch_settings_path()
+
+import neopixel as neopixel_stub  # noqa: E402
+
+
+def _ensure_src_symlinks():
+    """If flash root (``src``) has no ``patterns`` / ``presets.json``, link workspace copies."""
+    _ensure_workspace_dirs()
+    pat_ws = WORKSPACE / "patterns"
+    pat_link = DRIVER_SRC / "patterns"
+    if not pat_link.exists():
+        pat_link.symlink_to(pat_ws.resolve(), target_is_directory=True)
+    elif pat_link.is_symlink():
+        pass
+    # Real directory: treat as on-device flash (do not replace).
+
+    pr_ws = WORKSPACE / "presets.json"
+    if not pr_ws.is_file():
+        pr_ws.write_text("{}\n", encoding="utf-8")
+    pr_link = DRIVER_SRC / "presets.json"
+    if not pr_link.exists():
+        pr_link.symlink_to(pr_ws.resolve())
+
+
+class LedSimulatorApp:
+    def __init__(self):
+        _ensure_workspace_dirs()
+
+        self.root = tk.Tk()
+        self.root.title("led-simulator — led-driver (full app)")
+        self.root.minsize(640, 280)
+
+        self._pixel_queue: queue.Queue[list[tuple[int, int, int]] | None] = queue.Queue()
+        self._driver_thread: threading.Thread | None = None
+        self._driver_running = False
+        self._ws_port = tk.IntVar(value=8765)
+        self._status = tk.StringVar(
+            value="Idle — Start runs the full main.py (settings, presets, patterns/, /ws)."
+        )
+        self._canvas_leds: list[int] = []
+
+        self._build_ui()
+        self._install_pixel_sink()
+        self.root.after(50, self._pump_pixels)
+
+        self.root.protocol("WM_DELETE_WINDOW", self._on_quit)
+
+    def _build_ui(self):
+        top = ttk.Frame(self.root, padding=8)
+        top.pack(fill=tk.X)
+
+        row = ttk.Frame(top)
+        row.pack(fill=tk.X)
+
+        ttk.Button(row, text="Start", command=self._on_start).pack(side=tk.LEFT, padx=(0, 6))
+        ttk.Button(row, text="Stop", command=self._on_stop).pack(side=tk.LEFT, padx=(0, 16))
+        ttk.Label(row, text="HTTP / WS port:").pack(side=tk.LEFT)
+        ttk.Spinbox(row, from_=1024, to=65535, textvariable=self._ws_port, width=8).pack(
+            side=tk.LEFT, padx=4
+        )
+        ttk.Label(row, text="(Microdot; path /ws)").pack(side=tk.LEFT, padx=8)
+
+        hint = ttk.Label(
+            top,
+            text=(
+                "Flash root is led-driver/src: edit workspace/settings.json, presets.json, "
+                "and patterns/ (or use files already under src/)."
+            ),
+            wraplength=620,
+            justify=tk.LEFT,
+        )
+        hint.pack(fill=tk.X, pady=(8, 0))
+
+        self._canvas = tk.Canvas(self.root, height=120, background="#1a1a1a", highlightthickness=0)
+        self._canvas.pack(fill=tk.BOTH, expand=True, padx=8, pady=(0, 8))
+
+        st = ttk.Label(self.root, textvariable=self._status, padding=(8, 0, 8, 8))
+        st.pack(fill=tk.X)
+
+    def _install_pixel_sink(self):
+        def sink(buf: list[tuple[int, int, int]]):
+            self._pixel_queue.put(buf)
+
+        neopixel_stub.PIXEL_SINK = sink
+
+    def _pump_pixels(self):
+        try:
+            while True:
+                buf = self._pixel_queue.get_nowait()
+                if buf is None:
+                    self._draw_leds([(0, 0, 0)] * max(1, len(self._canvas_leds)))
+                else:
+                    self._draw_leds(buf)
+        except queue.Empty:
+            pass
+        self.root.after(50, self._pump_pixels)
+
+    def _draw_leds(self, buf: list[tuple[int, int, int]]):
+        self._canvas.delete("led")
+        n = len(buf)
+        if n == 0:
+            return
+        cw = self._canvas.winfo_width() or 700
+        margin = 12
+        usable = max(40, cw - 2 * margin)
+        gap = 4
+        diam = max(6, min(22, (usable - (n - 1) * gap) // n))
+        y = 50
+        total_w = n * diam + (n - 1) * gap
+        x0 = max(margin, (cw - total_w) // 2)
+        self._canvas_leds = []
+        for i, (r, g, b) in enumerate(buf):
+            x = x0 + i * (diam + gap)
+            fill = f"#{r:02x}{g:02x}{b:02x}"
+            outline = "#444444" if (r + g + b) > 40 else "#666666"
+            oid = self._canvas.create_oval(
+                x, y, x + diam, y + diam, fill=fill, outline=outline, width=1, tags="led"
+            )
+            self._canvas_leds.append(oid)
+
+    def _run_main_py_thread(self, port: int):
+        try:
+            try:
+                import led_driver_sim_hook as sim_hook
+
+                sim_hook.clear_app()
+            except ImportError:
+                pass
+
+            os.environ["LED_SIM_PORT"] = str(port)
+            os.environ["LED_SIM_ROOT"] = str(SIM_ROOT)
+
+            runpy.run_path(str(DRIVER_MAIN), run_name="__main__")
+        except Exception as ex:  # noqa: BLE001
+            self.root.after(0, lambda e=ex: messagebox.showerror("Simulator", str(e)))
+        finally:
+            for key in ("LED_SIM_PORT", "LED_SIM_ROOT"):
+                os.environ.pop(key, None)
+            try:
+                import led_driver_sim_hook as sim_hook
+
+                sim_hook.clear_app()
+            except ImportError:
+                pass
+            self._driver_running = False
+            self._pixel_queue.put(None)
+            self.root.after(0, lambda: self._status.set("Stopped."))
+
+    def _on_start(self):
+        if self._driver_running:
+            messagebox.showwarning("Simulator", "Already running — press Stop first.")
+            return
+
+        for k in list(sys.modules):
+            if k.startswith("patterns."):
+                del sys.modules[k]
+
+        _ensure_src_symlinks()
+        os.chdir(DRIVER_SRC)
+
+        port = int(self._ws_port.get())
+        self._driver_running = True
+        self.root.after(
+            0,
+            lambda p=port: self._status.set(
+                f"Running full app (main.py) — ws://127.0.0.1:{p}/ws"
+            ),
+        )
+
+        self._driver_thread = threading.Thread(
+            target=self._run_main_py_thread,
+            args=(port,),
+            daemon=True,
+        )
+        self._driver_thread.start()
+
+    def _on_stop(self):
+        try:
+            import led_driver_sim_hook as sim_hook
+
+            app = sim_hook.get_app()
+            if app is not None and getattr(app, "server", None):
+                app.shutdown()
+        except ImportError:
+            pass
+
+    def _on_quit(self):
+        self._on_stop()
+        self.root.destroy()
+
+    def run(self):
+        self.root.mainloop()
+
+
+def main():
+    if not DRIVER_SRC.is_dir() or not DRIVER_MAIN.is_file():
+        print("led-driver/src/main.py not found next to led-simulator.", file=sys.stderr)
+        sys.exit(1)
+    if not DRIVER_LIB.is_dir():
+        print("led-driver/lib not found next to led-simulator.", file=sys.stderr)
+        sys.exit(1)
+    app = LedSimulatorApp()
+    app.run()
+
+
+if __name__ == "__main__":
+    main()
diff --git a/led_driver_sim_hook.py b/led_driver_sim_hook.py
new file mode 100644
index 0000000..174018c
--- /dev/null
+++ b/led_driver_sim_hook.py
@@ -0,0 +1,17 @@
+"""Host-only: led-simulator registers the Microdot app so Stop can call shutdown()."""
+
+_app = None
+
+
+def register_app(app):
+    global _app
+    _app = app
+
+
+def get_app():
+    return _app
+
+
+def clear_app():
+    global _app
+    _app = None
diff --git a/settings.default.json b/settings.default.json
new file mode 100644
index 0000000..c802665
--- /dev/null
+++ b/settings.default.json
@@ -0,0 +1,13 @@
+{
+  "led_pin": 10,
+  "num_leds": 32,
+  "color_order": "rgb",
+  "name": "sim",
+  "debug": false,
+  "default": "on",
+  "brightness": 255,
+  "transport_type": "wifi",
+  "wifi_channel": 1,
+  "ssid": "",
+  "password": ""
+}
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diff --git a/stubs/__pycache__/ubinascii.cpython-313.pyc b/stubs/__pycache__/ubinascii.cpython-313.pyc
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diff --git a/stubs/__pycache__/utime.cpython-313.pyc b/stubs/__pycache__/utime.cpython-313.pyc
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diff --git a/stubs/machine.py b/stubs/machine.py
new file mode 100644
index 0000000..d4d00bc
--- /dev/null
+++ b/stubs/machine.py
@@ -0,0 +1,18 @@
+"""CPython stub for MicroPython `machine` (led-simulator)."""
+
+
+class Pin:
+    OUT = 1
+    IN = 0
+
+    def __init__(self, pin_id, mode=None, *, pull=None, value=None):
+        self.id = pin_id
+        self.mode = mode
+
+
+class WDT:
+    def __init__(self, timeout=10000):
+        self._timeout = timeout
+
+    def feed(self):
+        pass
diff --git a/stubs/neopixel.py b/stubs/neopixel.py
new file mode 100644
index 0000000..36f2213
--- /dev/null
+++ b/stubs/neopixel.py
@@ -0,0 +1,37 @@
+"""Host NeoPixel: keeps RGB buffer and notifies the GUI on `write()`."""
+
+# Set by led-simulator main: callable(list[tuple[int,int,int]]) -> None
+PIXEL_SINK = None
+
+
+class NeoPixel:
+    def __init__(self, pin, n):
+        self.pin = pin
+        self.n = n
+        self._buf = [(0, 0, 0)] * n
+
+    def __setitem__(self, index, value):
+        if isinstance(value, (list, tuple)) and len(value) >= 3:
+            r, g, b = (int(value[0]), int(value[1]), int(value[2]))
+            self._buf[index] = (
+                max(0, min(255, r)),
+                max(0, min(255, g)),
+                max(0, min(255, b)),
+            )
+
+    def __getitem__(self, index):
+        return self._buf[index]
+
+    def fill(self, color):
+        c = (0, 0, 0)
+        if isinstance(color, (list, tuple)) and len(color) >= 3:
+            c = (
+                max(0, min(255, int(color[0]))),
+                max(0, min(255, int(color[1]))),
+                max(0, min(255, int(color[2]))),
+            )
+        self._buf = [c] * self.n
+
+    def write(self):
+        if PIXEL_SINK is not None:
+            PIXEL_SINK(list(self._buf))
diff --git a/stubs/network.py b/stubs/network.py
new file mode 100644
index 0000000..add5267
--- /dev/null
+++ b/stubs/network.py
@@ -0,0 +1,38 @@
+"""Minimal `network` stub so imports succeed (led-simulator)."""
+
+STA_IF = 0
+AP_IF = 1
+
+# Fixed “STA” identity for hello.py / discovery on the host.
+_SIM_MAC = b"\xaa\xbb\xcc\xdd\xee\xff"
+
+
+class WLAN:
+    PM_NONE = 0
+
+    def __init__(self, interface):
+        self._interface = interface
+        self._active = False
+
+    def active(self, is_active=None):
+        if is_active is None:
+            return self._active
+        self._active = bool(is_active)
+        return None
+
+    def config(self, param=None, **kwargs):
+        if param == "mac":
+            return _SIM_MAC
+        return None
+
+    def connect(self, *args, **kwargs):
+        return None
+
+    def isconnected(self):
+        return True
+
+    def ifconfig(self, config_tuple=None):
+        if config_tuple is None:
+            # ip, subnet, gateway, dns — enough for hello UDP targets
+            return ("192.168.1.100", "255.255.255.0", "192.168.1.1", "8.8.8.8")
+        return None
diff --git a/stubs/ubinascii.py b/stubs/ubinascii.py
new file mode 100644
index 0000000..b78bb5c
--- /dev/null
+++ b/stubs/ubinascii.py
@@ -0,0 +1,6 @@
+"""Map MicroPython `ubinascii` to CPython `binascii`."""
+
+import binascii
+
+hexlify = binascii.hexlify
+unhexlify = binascii.unhexlify
diff --git a/stubs/utime.py b/stubs/utime.py
new file mode 100644
index 0000000..1ed55e5
--- /dev/null
+++ b/stubs/utime.py
@@ -0,0 +1,22 @@
+"""CPython stub for MicroPython `utime` (led-simulator)."""
+
+import time
+
+_MS_MASK = (1 << 30) - 1
+
+
+def sleep_ms(ms):
+    time.sleep(max(0, ms) / 1000.0)
+
+
+def sleep(s):
+    time.sleep(s)
+
+
+def ticks_ms():
+    return int(time.monotonic() * 1000) & _MS_MASK
+
+
+def ticks_diff(t1, t0):
+    """Approximate MicroPython ticks_diff for host monotonic ms."""
+    return ((t1 - t0 + (1 << 29)) & _MS_MASK) - (1 << 29)
diff --git a/workspace/patterns/.gitkeep b/workspace/patterns/.gitkeep
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/workspace/patterns/.gitkeep
@@ -0,0 +1 @@
+
diff --git a/workspace/patterns/__init__.py b/workspace/patterns/__init__.py
new file mode 100644
index 0000000..3885a94
--- /dev/null
+++ b/workspace/patterns/__init__.py
@@ -0,0 +1 @@
+# Host package mirror of device flash `patterns/` (pattern modules).