diff --git a/packages/playground/website/vite.config.ts b/packages/playground/website/vite.config.ts
index 94ed3fd326..4c3015e34c 100644
--- a/packages/playground/website/vite.config.ts
+++ b/packages/playground/website/vite.config.ts
@@ -17,6 +17,7 @@ import {
 } from '../build-config';
 // eslint-disable-next-line @nx/enforce-module-boundaries
 import { oAuthMiddleware } from './vite.oauth';
+import { serveClientLibrary } from './vite.serve-client-library';
 import { exec as execCb } from 'node:child_process';
 import { promisify } from 'node:util';
 import { fileURLToPath } from 'node:url';
@@ -190,6 +191,7 @@ export default defineConfig(({ command, mode }) => {
 					server.middlewares.use(oAuthMiddleware);
 				},
 			},
+			serveClientLibrary(),
 			/**
 			 * Copy the `.htaccess` file to the `dist` directory.
 			 */
diff --git a/packages/playground/website/vite.serve-client-library.ts b/packages/playground/website/vite.serve-client-library.ts
new file mode 100644
index 0000000000..c030a9e17c
--- /dev/null
+++ b/packages/playground/website/vite.serve-client-library.ts
@@ -0,0 +1,162 @@
+/**
+ * Vite plugin that serves the built @wp-playground/client library at
+ * /client/ during development, matching production where
+ * playground.wordpress.net/client/index.js is available.
+ *
+ * Auto-builds the client if missing and triggers a rebuild when source
+ * files change (detected via Vite's file watcher).
+ */
+import type { Plugin, ViteDevServer } from 'vite';
+import { existsSync, readFileSync, readdirSync, statSync } from 'node:fs';
+import { join, resolve, relative, isAbsolute } from 'node:path';
+import { exec } from 'node:child_process';
+
+export function serveClientLibrary(): Plugin {
+	return {
+		name: 'serve-client-library',
+		configureServer(server: ViteDevServer) {
+			const repoRoot = join(__dirname, '../../../');
+			const clientDistDir = join(
+				repoRoot,
+				'dist/packages/playground/client'
+			);
+			const clientSrcDir = join(__dirname, '../client/src');
+			let buildInProgress = false;
+			let stalenessChecked = false;
+			let sourcesDirty = false;
+
+			function newestMtimeIn(dir: string): number {
+				let newest = 0;
+				try {
+					for (const entry of readdirSync(dir, {
+						withFileTypes: true,
+					})) {
+						const full = join(dir, entry.name);
+						if (entry.isDirectory()) {
+							newest = Math.max(newest, newestMtimeIn(full));
+						} else if (entry.isFile()) {
+							newest = Math.max(newest, statSync(full).mtimeMs);
+						}
+					}
+				} catch {
+					// Directory may not exist yet
+				}
+				return newest;
+			}
+
+			function triggerClientBuild() {
+				if (buildInProgress) {
+					return;
+				}
+				buildInProgress = true;
+				server.config.logger.warn(
+					'\n  Building @wp-playground/client… Refresh when done.\n'
+				);
+				exec(
+					'npx nx build playground-client',
+					{ cwd: repoRoot },
+					(error, stdout, stderr) => {
+						buildInProgress = false;
+						stalenessChecked = true;
+						sourcesDirty = false;
+						if (error) {
+							server.config.logger.error(
+								'  @wp-playground/client build failed. ' +
+									'Run manually: npx nx build playground-client\n'
+							);
+							if (stderr) {
+								server.config.logger.error(stderr);
+							}
+						} else {
+							server.config.logger.info(
+								'  @wp-playground/client built. Refresh to load.\n'
+							);
+						}
+					}
+				);
+			}
+
+			server.watcher.add(clientSrcDir);
+			server.watcher.on('all', (_event, changedPath) => {
+				const rel = relative(clientSrcDir, changedPath);
+				if (!rel.startsWith('..') && !isAbsolute(rel)) {
+					sourcesDirty = true;
+					stalenessChecked = false;
+				}
+			});
+
+			server.middlewares.use((req, res, next) => {
+				if (!req.url?.startsWith('/client/')) {
+					return next();
+				}
+
+				const distIndexPath = join(clientDistDir, 'index.js');
+
+				if (!existsSync(distIndexPath)) {
+					triggerClientBuild();
+					res.setHeader('Access-Control-Allow-Origin', '*');
+					res.setHeader('Content-Type', 'application/javascript');
+					res.statusCode = 503;
+					res.end(
+						'throw new Error(' +
+							'"@wp-playground/client is not built yet. ' +
+							'A build was triggered automatically — refresh in a few seconds.\\n' +
+							'Or build manually: npx nx build playground-client"' +
+							');'
+					);
+					return;
+				}
+
+				if (!stalenessChecked && !buildInProgress) {
+					stalenessChecked = true;
+					const distMtime = statSync(distIndexPath).mtimeMs;
+					const srcMtime = newestMtimeIn(clientSrcDir);
+					if (srcMtime > distMtime) {
+						sourcesDirty = true;
+					}
+				}
+				if (sourcesDirty && !buildInProgress) {
+					sourcesDirty = false;
+					triggerClientBuild();
+				}
+
+				let urlPath: string;
+				try {
+					urlPath = new URL(req.url, 'http://localhost').pathname;
+				} catch {
+					res.statusCode = 400;
+					res.end('Invalid request URL');
+					return;
+				}
+				const filePath = resolve(
+					clientDistDir,
+					urlPath.slice('/client/'.length)
+				);
+				const rel = relative(clientDistDir, filePath);
+				if (rel.startsWith('..') || isAbsolute(rel)) {
+					res.statusCode = 403;
+					res.end();
+					return;
+				}
+				if (!existsSync(filePath) || statSync(filePath).isDirectory()) {
+					return next();
+				}
+				const contentTypes: Record<string, string> = {
+					'.js': 'application/javascript',
+					'.cjs': 'application/javascript',
+					'.json': 'application/json',
+					'.map': 'application/json',
+				};
+				const ext = Object.keys(contentTypes).find((e) =>
+					filePath.endsWith(e)
+				);
+				res.setHeader('Access-Control-Allow-Origin', '*');
+				res.setHeader(
+					'Content-Type',
+					ext ? contentTypes[ext] : 'application/octet-stream'
+				);
+				res.end(readFileSync(filePath));
+			});
+		},
+	};
+}