diff --git a/README.md b/README.md
index 5774223..0661357 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,13 @@ Status: milestone 2, thin API + parity page done.
 
 ## Development
 
-Two terminals:
+One command (installs frontend deps on first run, Ctrl-C stops everything):
+
+```sh
+./dev.sh
+```
+
+Or manually, in two terminals:
 
 ```sh
 go run ./cmd/spreadlab        # API on localhost:8080
diff --git a/dev.sh b/dev.sh
new file mode 100755
index 0000000..131c26f
--- /dev/null
+++ b/dev.sh
@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Local dev stack in one command:
+#   - Go API on localhost:8080
+#   - Vite dev server on localhost:5173 (proxies /api to the Go server)
+# One Ctrl-C stops everything; if either server dies, the other is stopped.
+set -euo pipefail
+
+cd "$(dirname "$0")"
+
+if [ ! -d web/node_modules ]; then
+  echo "dev.sh: first run, installing frontend dependencies..."
+  (cd web && npm install)
+fi
+
+# On exit (Ctrl-C included), stop whichever background job is still running.
+trap 'kill $(jobs -p) 2>/dev/null' EXIT
+
+go run ./cmd/spreadlab &
+(cd web && npm run dev) &
+
+# wait -n returns when the FIRST job exits; the trap then cleans up the rest.
+wait -n