diff --git a/scripts/launch-dev.sh b/scripts/launch-dev.sh
new file mode 100644
index 0000000..0c0f3f4
--- /dev/null
+++ b/scripts/launch-dev.sh
@@ -0,0 +1,131 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT="${MOUSEHOLD_ROOT:-/mnt/DATA/git/mousehold}"
+PYTHON="${PYTHON:-$ROOT/.venv/bin/python}"
+NPM="${NPM:-npm}"
+BACKEND_HOST="${MOUSEHOLD_BACKEND_HOST:-127.0.0.1}"
+BACKEND_PORT="${MOUSEHOLD_BACKEND_PORT:-8000}"
+FRONTEND_HOST="${MOUSEHOLD_FRONTEND_HOST:-127.0.0.1}"
+FRONTEND_PORT="${MOUSEHOLD_FRONTEND_PORT:-5173}"
+OPEN_BROWSER="${OPEN_BROWSER:-1}"
+
+LOG_DIR="$ROOT/data/dev-launcher"
+BACKEND_LOG="$LOG_DIR/backend.log"
+FRONTEND_LOG="$LOG_DIR/frontend.log"
+BACKEND_URL="http://$BACKEND_HOST:$BACKEND_PORT"
+FRONTEND_URL="http://$FRONTEND_HOST:$FRONTEND_PORT"
+
+backend_pid=""
+frontend_pid=""
+
+fail() {
+  printf 'launch-dev: %s\n' "$*" >&2
+  exit 1
+}
+
+port_is_free() {
+  "$PYTHON" - "$1" "$2" <<'PY'
+import socket
+import sys
+
+host = sys.argv[1]
+port = int(sys.argv[2])
+with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
+    sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    try:
+        sock.bind((host, port))
+    except OSError:
+        raise SystemExit(1)
+PY
+}
+
+wait_for_url() {
+  "$PYTHON" - "$1" <<'PY'
+import sys
+import time
+import urllib.request
+
+url = sys.argv[1]
+deadline = time.monotonic() + 60
+last_error = None
+while time.monotonic() < deadline:
+    try:
+        with urllib.request.urlopen(url, timeout=2) as response:
+            if 200 <= response.status < 500:
+                raise SystemExit(0)
+    except Exception as exc:  # noqa: BLE001 - printed only on timeout.
+        last_error = exc
+    time.sleep(1)
+print(f"Timed out waiting for {url}: {last_error}", file=sys.stderr)
+raise SystemExit(1)
+PY
+}
+
+cleanup() {
+  if [ -n "${frontend_pid:-}" ] && kill -0 "$frontend_pid" 2>/dev/null; then
+    kill "$frontend_pid" 2>/dev/null || true
+  fi
+  if [ -n "${backend_pid:-}" ] && kill -0 "$backend_pid" 2>/dev/null; then
+    kill "$backend_pid" 2>/dev/null || true
+  fi
+}
+trap cleanup EXIT INT TERM
+
+[ -x "$PYTHON" ] || fail "Python virtualenv not found at $PYTHON. Run: cd $ROOT && python -m venv .venv && . .venv/bin/activate && pip install -r requirements-dev.txt && pip install -e ."
+command -v "$NPM" >/dev/null 2>&1 || fail "npm not found. Install Node.js/npm, then rerun this launcher."
+[ -d "$ROOT/node_modules" ] || fail "node_modules missing. Run: cd $ROOT && npm install"
+
+mkdir -p "$LOG_DIR"
+: > "$BACKEND_LOG"
+: > "$FRONTEND_LOG"
+
+port_is_free "$BACKEND_HOST" "$BACKEND_PORT" || fail "$BACKEND_URL is already in use"
+port_is_free "$FRONTEND_HOST" "$FRONTEND_PORT" || fail "$FRONTEND_URL is already in use"
+
+printf 'Starting Mousehold API at %s\n' "$BACKEND_URL"
+(
+  cd "$ROOT"
+  "$PYTHON" -m uvicorn mousehold_api.main:app --host "$BACKEND_HOST" --port "$BACKEND_PORT" --reload
+) >"$BACKEND_LOG" 2>&1 &
+backend_pid="$!"
+
+printf 'Waiting for %s/health\n' "$BACKEND_URL"
+wait_for_url "$BACKEND_URL/health" || {
+  tail -n 80 "$BACKEND_LOG" >&2 || true
+  fail "backend did not become healthy"
+}
+
+printf 'Starting Mousehold Web UI at %s\n' "$FRONTEND_URL"
+(
+  cd "$ROOT/apps/web"
+  "$NPM" run dev -- --host "$FRONTEND_HOST" --port "$FRONTEND_PORT"
+) >"$FRONTEND_LOG" 2>&1 &
+frontend_pid="$!"
+
+printf 'Waiting for %s\n' "$FRONTEND_URL"
+wait_for_url "$FRONTEND_URL" || {
+  tail -n 80 "$FRONTEND_LOG" >&2 || true
+  fail "frontend did not become reachable"
+}
+
+if [ "$OPEN_BROWSER" = "1" ] && command -v xdg-open >/dev/null 2>&1; then
+  xdg-open "$FRONTEND_URL" >/dev/null 2>&1 || true
+fi
+
+cat <<EOF
+
+Mousehold is running.
+Web UI:  $FRONTEND_URL
+API:     $BACKEND_URL
+Health:  $BACKEND_URL/health
+Docs:    $BACKEND_URL/docs
+
+Logs:
+Backend: $BACKEND_LOG
+Web UI:  $FRONTEND_LOG
+
+Press Ctrl+C to stop both processes.
+EOF
+
+wait