diff --git a/start-dev.bat b/start-dev.bat
new file mode 100644
index 0000000..d674961
--- /dev/null
+++ b/start-dev.bat
@@ -0,0 +1,54 @@
+@echo off
+REM Starts backend (NestJS) and frontend (Svelte/Vite) in separate windows.
+REM Run this file from the repo root by double-clicking or from a terminal.
+
+setlocal ENABLEDELAYEDEXPANSION
+
+call :detectPM backend BACKEND_PM
+call :detectPM frontend FRONTEND_PM
+
+echo Detected package manager (backend): %BACKEND_PM%
+echo Detected package manager (frontend): %FRONTEND_PM%
+
+echo Installing dependencies if needed...
+call :install backend %BACKEND_PM%
+call :install frontend %FRONTEND_PM%
+
+REM Set backend environment variables (edit as needed)
+set "SERIAL_PORT=COM4"
+set "SERIAL_BAUD=115200"
+echo Using SERIAL_PORT=%SERIAL_PORT% SERIAL_BAUD=%SERIAL_BAUD%
+
+echo Launching backend (watch)...
+start "backend" cmd /k "cd /d %~dp0backend && set SERIAL_PORT=%SERIAL_PORT% && set SERIAL_BAUD=%SERIAL_BAUD% && %BACKEND_PM% run start:dev"
+
+echo Launching frontend (Vite dev)...
+start "frontend" cmd /k "cd /d %~dp0frontend && %FRONTEND_PM% run dev"
+
+echo Both processes started in their own windows.
+exit /b 0
+
+:detectPM
+REM %1 = folder, %2 = out var name
+set FOLDER=%1
+set OUTVAR=%2
+set PM=
+if exist "%FOLDER%\pnpm-lock.yaml" set PM=pnpm
+if exist "%FOLDER%\yarn.lock" set PM=yarn
+if exist "%FOLDER%\package-lock.json" set PM=npm
+if not defined PM set PM=npm
+for /f "delims=" %%A in ("%PM%") do set %OUTVAR%=%%A
+exit /b 0
+
+:install
+REM %1 = folder, %2 = pm
+pushd %1 >nul 2>&1
+if /i "%2"=="npm" (
+  if not exist node_modules (echo Installing %1 deps with npm... & npm install --no-audit --no-fund)
+) else if /i "%2"=="pnpm" (
+  if not exist node_modules (echo Installing %1 deps with pnpm... & pnpm install)
+) else if /i "%2"=="yarn" (
+  if not exist node_modules (echo Installing %1 deps with yarn... & yarn install)
+)
+popd >nul 2>&1
+exit /b 0