diff --git a/package-lock.json b/package-lock.json
index 785994d8..f1ff1701 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -33110,6 +33110,7 @@
         "@rollup/plugin-html": "^2.0.0",
         "@types/node": "^20.19.43",
         "html-webpack-plugin": "^5.6.8",
+        "playwright": "^1.61.0",
         "rolldown": "^1.2.5",
         "rollup": "^4.62.4",
         "tsup": "^8.5.1",
diff --git a/packages/unplugin-skew-protection/package.json b/packages/unplugin-skew-protection/package.json
index f59e9570..dacf91e8 100644
--- a/packages/unplugin-skew-protection/package.json
+++ b/packages/unplugin-skew-protection/package.json
@@ -47,6 +47,7 @@
     "@rollup/plugin-html": "^2.0.0",
     "@types/node": "^20.19.43",
     "html-webpack-plugin": "^5.6.8",
+    "playwright": "^1.61.0",
     "rolldown": "^1.2.5",
     "rollup": "^4.62.4",
     "tsup": "^8.5.1",
diff --git a/packages/unplugin-skew-protection/test/e2e/browser.test.ts b/packages/unplugin-skew-protection/test/e2e/browser.test.ts
new file mode 100644
index 00000000..f53e391d
--- /dev/null
+++ b/packages/unplugin-skew-protection/test/e2e/browser.test.ts
@@ -0,0 +1,109 @@
+import { join } from 'node:path'
+import { rm } from 'node:fs/promises'
+
+import { afterAll, beforeAll, describe, expect, test } from 'vitest'
+import { chromium, type Browser } from 'playwright'
+
+import { BUNDLERS, TOKEN, createFixture } from '../support/builders.js'
+import { serveStatic, type StaticServer } from '../support/serve.js'
+
+const EXPECTED_QUERY = `?nfdpl=${TOKEN}`
+
+let browser: Browser
+
+beforeAll(async () => {
+  browser = await chromium.launch()
+})
+
+afterAll(async () => {
+  await browser.close()
+})
+
+describe.each(BUNDLERS)('$name', ({ build, expectedUnstamped }) => {
+  let root: string
+  let server: StaticServer
+
+  beforeAll(async () => {
+    root = await createFixture()
+    const outDir = join(root, 'dist')
+    await build(root, outDir)
+    server = await serveStatic(outDir)
+  })
+
+  afterAll(async () => {
+    await server.close()
+    await rm(root, { force: true, recursive: true })
+  })
+
+  test('serves an app whose asset requests are pinned to the deploy', async () => {
+    const page = await browser.newPage()
+    const assetRequests: URL[] = []
+    const failedResponses: string[] = []
+
+    page.on('request', (request) => {
+      const url = new URL(request.url())
+
+      if (/\.(css|js|mjs)$/.test(url.pathname)) {
+        assetRequests.push(url)
+      }
+    })
+
+    page.on('response', (response) => {
+      // The browser asks for a favicon that the fixture does not ship; every other 4xx/5xx
+      // means a stamped URL failed to resolve, which is the failure mode worth catching.
+      if (response.status() >= 400 && !response.url().endsWith('/favicon.ico')) {
+        failedResponses.push(`${String(response.status())} ${response.url()}`)
+      }
+    })
+
+    try {
+      await page.goto(`${server.url}/`)
+
+      // The fixture marks `data-state` on both the success and failure paths, so a chunk that
+      // never loads is reported as a soft failure here instead of stalling the whole test --
+      // which keeps the assertions below running and shows every problem in one go.
+      const reachedTerminalState = await page
+        .waitForSelector('#app[data-state]', { timeout: 10_000 })
+        .then(() => true)
+        .catch(() => false)
+
+      expect
+        .soft(reachedTerminalState, 'the app never finished loading: its dynamic import neither resolved nor rejected')
+        .toBe(true)
+
+      expect
+        .soft(
+          failedResponses,
+          'the page requested assets that the server could not serve, so a stamped URL does not point at a file this build emitted',
+        )
+        .toEqual([])
+
+      expect
+        .soft(
+          await page.textContent('#app'),
+          'the lazily imported chunk did not evaluate in the browser, so its stamped specifier does not resolve to a working module',
+        )
+        .toBe('lazy chunk loaded')
+
+      const unstamped = assetRequests.filter((url) => url.search !== EXPECTED_QUERY).map((url) => url.pathname)
+      expect
+        .soft(
+          unstamped,
+          'these assets were requested without the deploy-pinning query parameter, so they are not pinned to this deploy',
+        )
+        .toEqual(expectedUnstamped)
+
+      // Guards against a vacuous pass: with no asset requests at all, the comparison above is
+      // satisfied by an empty list for the bundlers that are expected to stamp everything.
+      const stamped = assetRequests.filter((url) => url.search === EXPECTED_QUERY).map((url) => url.pathname)
+      expect
+        .soft(
+          stamped.length,
+          `no asset was requested with the deploy-pinning query parameter (all requests: ${assetRequests.map((url) => url.pathname).join(', ') || 'none'})`,
+        )
+        .toBeGreaterThan(0)
+    } finally {
+      await page.close()
+    }
+  })
+})
diff --git a/packages/unplugin-skew-protection/test/fixtures/entry.js b/packages/unplugin-skew-protection/test/fixtures/entry.js
new file mode 100644
index 00000000..0ec14abf
--- /dev/null
+++ b/packages/unplugin-skew-protection/test/fixtures/entry.js
@@ -0,0 +1,21 @@
+// Bundlers that generate their own HTML may not carry the fixture's markup, so the mount
+// point is created here when the page does not already provide one.
+let app = document.querySelector('#app')
+
+if (!app) {
+  app = document.createElement('div')
+  app.id = 'app'
+  document.body.prepend(app)
+}
+
+app.textContent = 'entry loaded'
+
+import('./lazy.js')
+  .then(({ default: message }) => {
+    app.textContent = message
+    app.dataset.state = 'loaded'
+  })
+  .catch((error) => {
+    app.textContent = `failed: ${error.message}`
+    app.dataset.state = 'failed'
+  })
diff --git a/packages/unplugin-skew-protection/test/fixtures/index.html b/packages/unplugin-skew-protection/test/fixtures/index.html
new file mode 100644
index 00000000..d4385e6e
--- /dev/null
+++ b/packages/unplugin-skew-protection/test/fixtures/index.html
@@ -0,0 +1,11 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8" />
+    <title>skew protection e2e</title>
+  </head>
+  <body>
+    <div id="app">loading</div>
+    <script type="module" src="./entry.js"></script>
+  </body>
+</html>
diff --git a/packages/unplugin-skew-protection/test/fixtures/lazy.js b/packages/unplugin-skew-protection/test/fixtures/lazy.js
new file mode 100644
index 00000000..68b7c47e
--- /dev/null
+++ b/packages/unplugin-skew-protection/test/fixtures/lazy.js
@@ -0,0 +1 @@
+export default 'lazy chunk loaded'
diff --git a/packages/unplugin-skew-protection/test/support/builders.ts b/packages/unplugin-skew-protection/test/support/builders.ts
new file mode 100644
index 00000000..48543546
--- /dev/null
+++ b/packages/unplugin-skew-protection/test/support/builders.ts
@@ -0,0 +1,122 @@
+import { copyFile, mkdtemp, readdir, readFile, writeFile } from 'node:fs/promises'
+import { fileURLToPath } from 'node:url'
+import { tmpdir } from 'node:os'
+import { dirname, join } from 'node:path'
+
+import HtmlWebpackPlugin from 'html-webpack-plugin'
+import webpack from 'webpack'
+import { build as viteBuild } from 'vite'
+import { rolldown } from 'rolldown'
+import { rollup } from 'rollup'
+import rollupHtmlPluginModule from '@rollup/plugin-html'
+
+import vitePlugin from '../../src/vite.js'
+import rollupPlugin from '../../src/rollup.js'
+import rolldownPlugin from '../../src/rolldown.js'
+import webpackPlugin from '../../src/webpack.js'
+
+// `@rollup/plugin-html` ships CJS-flavoured types for its ESM build, so under NodeNext the
+// default import is typed as the module namespace rather than the plugin factory.
+const rollupHtmlPlugin = rollupHtmlPluginModule as unknown as typeof rollupHtmlPluginModule.default
+
+export const TOKEN = 'e2e-token-123'
+
+const FIXTURE_DIR = join(dirname(fileURLToPath(import.meta.url)), '..', 'fixtures')
+
+export interface BundlerCase {
+  /**
+   * Asset paths that are expected to be served *without* the skew protection parameter.
+   *
+   * Only Vite and webpack expose an HTML hook to this plugin, so only they can pin the
+   * initial `<script>`. Plain Rollup and Rolldown emit no HTML, so the entry tag in a
+   * hand-authored page stays unpinned and only the dynamic import is stamped.
+   */
+  expectedUnstamped: string[]
+  build: (root: string, outDir: string) => Promise<void>
+  name: string
+}
+
+export async function createFixture(): Promise<string> {
+  const root = await mkdtemp(join(tmpdir(), 'skew-protection-e2e-'))
+  // The fixture is a flat directory, so copying file by file avoids `fs.cp`, which is still
+  // experimental below Node 22.3 and this package supports Node 20.
+  const entries = await readdir(FIXTURE_DIR)
+  await Promise.all(entries.map((entry) => copyFile(join(FIXTURE_DIR, entry), join(root, entry))))
+  return root
+}
+
+export const BUNDLERS: BundlerCase[] = [
+  {
+    name: 'vite',
+    expectedUnstamped: [],
+    build: async (root, outDir) => {
+      await viteBuild({
+        root,
+        logLevel: 'silent',
+        plugins: [vitePlugin({ baseDir: root, token: TOKEN })],
+        build: { outDir, emptyOutDir: true },
+      })
+    },
+  },
+  {
+    name: 'rollup',
+    expectedUnstamped: [],
+    build: async (root, outDir) => {
+      const bundle = await rollup({
+        input: join(root, 'entry.js'),
+        plugins: [rollupHtmlPlugin(), rollupPlugin({ baseDir: root, token: TOKEN })],
+      })
+      await bundle.write({ dir: outDir, format: 'es', entryFileNames: 'entry.js', chunkFileNames: '[name].js' })
+      await bundle.close()
+    },
+  },
+  {
+    name: 'rolldown',
+    expectedUnstamped: [],
+    build: async (root, outDir) => {
+      const bundle = await rolldown({
+        input: join(root, 'entry.js'),
+        plugins: [rollupHtmlPlugin(), rolldownPlugin({ baseDir: root, token: TOKEN })],
+      })
+      await bundle.write({ dir: outDir, format: 'es', entryFileNames: 'entry.js', chunkFileNames: '[name].js' })
+      await bundle.close()
+    },
+  },
+  {
+    name: 'webpack',
+    expectedUnstamped: [],
+    build: async (root, outDir) => {
+      // html-webpack-plugin injects its own tag for the entry, so the template must not carry
+      // the fixture's `<script src="./entry.js">` as well.
+      const template = join(root, 'template.html')
+      const html = await readFile(join(root, 'index.html'), 'utf8')
+      await writeFile(template, html.replace(/\s*<script\b[^>]*><\/script>/i, ''))
+
+      await new Promise<void>((resolve, reject) => {
+        webpack(
+          {
+            context: root,
+            entry: join(root, 'entry.js'),
+            mode: 'production',
+            optimization: { minimize: false },
+            output: { chunkFilename: '[name].chunk.js', filename: 'main.js', path: outDir },
+            plugins: [new HtmlWebpackPlugin({ template }), webpackPlugin({ baseDir: root, token: TOKEN })],
+          },
+          (err, stats) => {
+            if (err) {
+              reject(err)
+              return
+            }
+
+            if (stats?.hasErrors()) {
+              reject(new Error(stats.toString({ errorDetails: true })))
+              return
+            }
+
+            resolve()
+          },
+        )
+      })
+    },
+  },
+]
diff --git a/packages/unplugin-skew-protection/test/support/serve.ts b/packages/unplugin-skew-protection/test/support/serve.ts
new file mode 100644
index 00000000..8847ceff
--- /dev/null
+++ b/packages/unplugin-skew-protection/test/support/serve.ts
@@ -0,0 +1,69 @@
+import { createServer, type Server } from 'node:http'
+import { readFile } from 'node:fs/promises'
+import { join, normalize } from 'node:path'
+
+const CONTENT_TYPES: Record<string, string> = {
+  '.css': 'text/css',
+  '.html': 'text/html',
+  '.js': 'text/javascript',
+  '.mjs': 'text/javascript',
+}
+
+export interface StaticServer {
+  close: () => Promise<void>
+  url: string
+}
+
+/**
+ * Serves `root` over HTTP for the duration of a test. The query string is ignored when
+ * resolving a file, which is what makes the skew protection parameter transparent to a
+ * static host: `/assets/lazy-abc.js?nfdpl=token` has to serve `/assets/lazy-abc.js`.
+ */
+export async function serveStatic(root: string): Promise<StaticServer> {
+  const server = createServer((req, res) => {
+    // `req.url` is a path plus an optional query string, so a fixed base is enough to parse it.
+    const { pathname } = new URL(req.url ?? '/', 'http://localhost')
+    const relativePath = pathname === '/' ? 'index.html' : decodeURIComponent(pathname).replace(/^\/+/, '')
+
+    // Reject traversal outside the served directory rather than reading an arbitrary file.
+    if (normalize(relativePath).startsWith('..')) {
+      res.writeHead(403).end()
+      return
+    }
+
+    readFile(join(root, relativePath))
+      .then((body) => {
+        const extension = relativePath.slice(relativePath.lastIndexOf('.'))
+        res.writeHead(200, { 'content-type': CONTENT_TYPES[extension] ?? 'application/octet-stream' }).end(body)
+      })
+      .catch(() => {
+        res.writeHead(404).end()
+      })
+  })
+
+  await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve))
+
+  const address = server.address()
+
+  if (address === null || typeof address === 'string') {
+    throw new Error('static server did not bind to a TCP port')
+  }
+
+  return {
+    close: () => closeServer(server),
+    url: `http://127.0.0.1:${String(address.port)}`,
+  }
+}
+
+function closeServer(server: Server): Promise<void> {
+  return new Promise((resolve, reject) => {
+    server.close((error) => {
+      if (error) {
+        reject(error)
+        return
+      }
+
+      resolve()
+    })
+  })
+}
diff --git a/packages/unplugin-skew-protection/tsconfig.json b/packages/unplugin-skew-protection/tsconfig.json
index c54e97c5..26974433 100644
--- a/packages/unplugin-skew-protection/tsconfig.json
+++ b/packages/unplugin-skew-protection/tsconfig.json
@@ -8,10 +8,9 @@
     "moduleResolution": "NodeNext",
     "outDir": "./dist",
     "resolveJsonModule": true,
-    "rootDir": "./src",
     "skipLibCheck": true,
     "strict": true,
     "target": "ES2022"
   },
-  "include": ["src"]
+  "include": ["src", "test"]
 }
diff --git a/packages/unplugin-skew-protection/vitest.config.ts b/packages/unplugin-skew-protection/vitest.config.ts
index b255d0b4..34551675 100644
--- a/packages/unplugin-skew-protection/vitest.config.ts
+++ b/packages/unplugin-skew-protection/vitest.config.ts
@@ -5,5 +5,8 @@ export default defineConfig({
     env: {
       NO_COLOR: 'true',
     },
+    // The e2e suite builds the fixture with four bundlers and drives a real browser.
+    hookTimeout: 60_000,
+    testTimeout: 60_000,
   },
 })