diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 4a746e2b..9ff24ad1 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -52,3 +52,16 @@ Unit tests and end-to-end tests are available in the `tests/` folder.
     `npx playwright install --with-deps`
   - Run tests (Chromium only): `npm run test:e2e`
   - Run tests (Chromium, Firefox & Webkit): `npm run test:e2e:ci`
+
+## Previewing Pull Requests
+
+Active pull requests on the polyfill can be tested using the built version
+hosted within the preview environment.
+
+> **IMPORTANT**
+>
+> These previews are ephemeral, and will stop working after the pull request is
+> merged. Do not use this for any purpose other than testing the pull request.
+
+All polyfills are located at the root of the preview environment. For instance, the CommonJS functional version for PR 123 would be available at
+https://deploy-preview-123--anchor-polyfill.netlify.app/css-anchor-positioning-fn.umd.cjs.
diff --git a/netlify.toml b/netlify.toml
index 05169b68..6cb450a8 100644
--- a/netlify.toml
+++ b/netlify.toml
@@ -1,3 +1,8 @@
 [build]
   # If the $WPT_ONLY env var is set, only build branches that end with `--wpt-results`
   ignore = "if [[ ! $WPT_ONLY || $BRANCH == *--wpt-results ]]; then exit 1; else exit 0; fi"
+[[headers]]
+  for = "/css-anchor-positioning*" # Only allow for polyfill files
+  [headers.values]
+    access-control-allow-origin = "*"
+    content-type = "text/javascript"
diff --git a/package.json b/package.json
index 3e8df732..ceb8b2bd 100644
--- a/package.json
+++ b/package.json
@@ -49,10 +49,11 @@
     "package.json"
   ],
   "scripts": {
-    "build": "run-s build:dist build:fn",
+    "build": "run-s build:demo build:dist build:fn",
     "build:dist": "vite build",
     "build:fn": "cross-env BUILD_FN=1 vite build",
     "build:wpt": "cross-env BUILD_WPT=1 vite build",
+    "build:demo": "cross-env BUILD_DEMO=1 vite build",
     "preview": "vite preview",
     "serve": "vite dev",
     "tsc": "tsc --noEmit",
diff --git a/vite.config.ts b/vite.config.ts
index 0961f58c..7f1161b4 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -8,7 +8,7 @@ export default defineConfig({
   server: {
     port: 3000,
   },
-  build: process.env.NETLIFY
+  build: process.env.BUILD_DEMO
     ? {}
     : {
         lib: process.env.BUILD_WPT
@@ -35,7 +35,7 @@ export default defineConfig({
                 // the proper extensions will be added
                 fileName: 'css-anchor-positioning',
               },
-        emptyOutDir: !process.env.BUILD_FN,
+        emptyOutDir: false,
         target: 'es6',
         sourcemap: true,
         rollupOptions: {