diff --git a/extension/version.mjs b/extension/version.mjs
new file mode 100644
index 0000000..391191c
--- /dev/null
+++ b/extension/version.mjs
@@ -0,0 +1,10 @@
+export function updateState(installed, latest) {
+  const parse = value => typeof value === 'string' && /^\d+(\.\d+){0,3}$/.test(value) ? value.split('.').map(Number) : null;
+  const a = parse(installed), b = parse(latest);
+  if (!a || !b) return '';
+  for (let i = 0; i < 4; i++) {
+    if ((a[i] || 0) < (b[i] || 0)) return 'Update available';
+    if ((a[i] || 0) > (b[i] || 0)) return '';
+  }
+  return '';
+}