diff --git a/e2e/worker-engine.spec.ts b/e2e/worker-engine.spec.ts
new file mode 100644
index 0000000..68b6aea
--- /dev/null
+++ b/e2e/worker-engine.spec.ts
@@ -0,0 +1,47 @@
+/**
+ * Worker-mode guarantee: the package runs inside a Web Worker — the
+ * architecture every browser runtime entry point uses to keep
+ * conversions off the main thread. Imports via the CDN recipe pinned
+ * in interscript-ts/docs/CDN.md, so each CI run re-proves that recipe
+ * too.
+ */
+import { test, expect } from "@playwright/test"
+
+const CDN = "https://esm.sh/interscript@5.3.0"
+
+const WORKER_SOURCE = `
+  self.onmessage = async (event) => {
+    try {
+      const { configure, iscStrategy, transliterateAsync } = await import("${CDN}")
+      configure({
+        strategies: [iscStrategy({ baseUrl: "https://interscript.org/maps" })],
+      })
+      const output = await transliterateAsync("bgnpcgn-ukr-Cyrl-Latn-2019", event.data)
+      self.postMessage({ ok: true, output })
+    } catch (error) {
+      self.postMessage({ ok: false, error: String(error) })
+    }
+  }
+`
+
+test("the library converts inside a Web Worker via the CDN recipe", async ({ page }) => {
+  await page.goto("/")
+  const result = await page.evaluate(
+    async ({ source, input }) => {
+      const url = URL.createObjectURL(new Blob([source], { type: "text/javascript" }))
+      const worker = new Worker(url, { type: "module" })
+      try {
+        return await new Promise((resolve) => {
+          worker.onmessage = (event) => resolve(event.data)
+          worker.postMessage(input)
+        })
+      } finally {
+        worker.terminate()
+        URL.revokeObjectURL(url)
+      }
+    },
+    { source: WORKER_SOURCE, input: "Антон Олегович" },
+  )
+  expect(result.ok).toBe(true)
+  expect(result.output).toBe("Anton Olehovych")
+})