diff --git a/packages/cdn/src/demo.js b/packages/cdn/src/demo.js
index b46378d..56d8248 100644
--- a/packages/cdn/src/demo.js
+++ b/packages/cdn/src/demo.js
@@ -50,7 +50,12 @@ setTimeout(() => {
 		window.pageAgent = new PageAgent(config)
 	} else {
 		console.log('🚀 page-agent.js no current script detected, using default demo config')
-		window.pageAgent = new PageAgent()
+		const config = {
+			model: DEMO_MODEL,
+			baseURL: DEMO_BASE_URL,
+			apiKey: DEMO_API_KEY,
+		}
+		window.pageAgent = new PageAgent(config)
 	}
 
 	console.log('🚀 page-agent.js initialized with config:', window.pageAgent.config)
diff --git a/packages/llms/src/constants.ts b/packages/llms/src/constants.ts
index 36f5358..26b9629 100644
--- a/packages/llms/src/constants.ts
+++ b/packages/llms/src/constants.ts
@@ -1,20 +1,3 @@
-// Dev environment: use .env config if available, otherwise fallback to testing api
-export const DEFAULT_MODEL_NAME: string =
-	import.meta.env.DEV && import.meta.env.LLM_MODEL_NAME
-		? import.meta.env.LLM_MODEL_NAME
-		: 'PAGE-AGENT-FREE-TESTING-RANDOM'
-
-export const DEFAULT_API_KEY: string =
-	import.meta.env.DEV && import.meta.env.LLM_API_KEY
-		? import.meta.env.LLM_API_KEY
-		: 'PAGE-AGENT-FREE-TESTING-RANDOM'
-
-export const DEFAULT_BASE_URL: string =
-	import.meta.env.DEV && import.meta.env.LLM_BASE_URL
-		? import.meta.env.LLM_BASE_URL
-		: 'https://hwcxiuzfylggtcktqgij.supabase.co/functions/v1/llm-testing-proxy'
-
-// internal
-
+// Internal constants
 export const LLM_MAX_RETRIES = 2
 export const DEFAULT_TEMPERATURE = 0.7 // higher randomness helps auto-recovery
diff --git a/packages/llms/src/index.ts b/packages/llms/src/index.ts
index 3a79a17..6785b68 100644
--- a/packages/llms/src/index.ts
+++ b/packages/llms/src/index.ts
@@ -1,21 +1,23 @@
 import { OpenAIClient } from './OpenAIClient'
-import {
-	DEFAULT_API_KEY,
-	DEFAULT_BASE_URL,
-	DEFAULT_MODEL_NAME,
-	DEFAULT_TEMPERATURE,
-	LLM_MAX_RETRIES,
-} from './constants'
+import { DEFAULT_TEMPERATURE, LLM_MAX_RETRIES } from './constants'
 import { InvokeError } from './errors'
 import type { InvokeOptions, InvokeResult, LLMClient, LLMConfig, Message, Tool } from './types'
 
 export type { InvokeOptions, InvokeResult, LLMClient, LLMConfig, Message, Tool }
 
 export function parseLLMConfig(config: LLMConfig): Required<LLMConfig> {
+	// Runtime validation as defensive programming (types already guarantee these)
+	if (!config.baseURL || !config.apiKey || !config.model) {
+		throw new Error(
+			'[PageAgent] LLM configuration required. Please provide: baseURL, apiKey, model. ' +
+				'See: https://alibaba.github.io/page-agent/#/docs/features/models'
+		)
+	}
+
 	return {
-		baseURL: config.baseURL ?? DEFAULT_BASE_URL,
-		apiKey: config.apiKey ?? DEFAULT_API_KEY,
-		model: config.model ?? DEFAULT_MODEL_NAME,
+		baseURL: config.baseURL,
+		apiKey: config.apiKey,
+		model: config.model,
 		temperature: config.temperature ?? DEFAULT_TEMPERATURE,
 		maxRetries: config.maxRetries ?? LLM_MAX_RETRIES,
 		customFetch: (config.customFetch ?? fetch).bind(globalThis), // fetch will be illegal unless bound
diff --git a/packages/llms/src/types.ts b/packages/llms/src/types.ts
index f51bd45..a3f819b 100644
--- a/packages/llms/src/types.ts
+++ b/packages/llms/src/types.ts
@@ -87,9 +87,9 @@ export interface InvokeResult<TResult = unknown> {
  * LLM configuration
  */
 export interface LLMConfig {
-	baseURL?: string
-	apiKey?: string
-	model?: string
+	baseURL: string
+	apiKey: string
+	model: string
 
 	temperature?: number
 	maxRetries?: number
diff --git a/packages/page-agent/src/PageAgent.ts b/packages/page-agent/src/PageAgent.ts
index 1c6ca3c..e05b01d 100644
--- a/packages/page-agent/src/PageAgent.ts
+++ b/packages/page-agent/src/PageAgent.ts
@@ -95,7 +95,7 @@ export class PageAgent extends EventTarget {
 	/** History records */
 	history: AgentHistory[] = []
 
-	constructor(config: PageAgentConfig = {}) {
+	constructor(config: PageAgentConfig) {
 		super()
 
 		this.config = config
diff --git a/packages/page-agent/src/umd.ts b/packages/page-agent/src/umd.ts
index 58b7907..82f3a42 100644
--- a/packages/page-agent/src/umd.ts
+++ b/packages/page-agent/src/umd.ts
@@ -35,7 +35,12 @@ setTimeout(() => {
 		window.pageAgent = new PageAgent(config)
 	} else {
 		console.log('🚀 page-agent.js no current script detected, using default demo config')
-		window.pageAgent = new PageAgent()
+		const config: PageAgentConfig = {
+			model: DEMO_MODEL,
+			baseURL: DEMO_BASE_URL,
+			apiKey: DEMO_API_KEY,
+		}
+		window.pageAgent = new PageAgent(config)
 	}
 
 	console.log('🚀 page-agent.js initialized with config:', window.pageAgent.config)
diff --git a/packages/website/src/constants.ts b/packages/website/src/constants.ts
index 417853a..a20910c 100644
--- a/packages/website/src/constants.ts
+++ b/packages/website/src/constants.ts
@@ -7,3 +7,9 @@ export const CDN_DEMO_CN_URL =
 export const CDN_FULL_URL = 'https://cdn.jsdelivr.net/npm/@page-agent/cdn/dist/page-agent.js'
 export const CDN_FULL_CN_URL =
 	'https://registry.npmmirror.com/@page-agent/cdn/latest/files/dist/page-agent.js'
+
+// Demo LLM for website testing
+export const DEMO_MODEL = 'PAGE-AGENT-FREE-TESTING-RANDOM'
+export const DEMO_BASE_URL =
+	'https://hwcxiuzfylggtcktqgij.supabase.co/functions/v1/llm-testing-proxy'
+export const DEMO_API_KEY = 'PAGE-AGENT-FREE-TESTING-RANDOM'
diff --git a/packages/website/src/pages/Home.tsx b/packages/website/src/pages/Home.tsx
index dcd02c1..5b466c5 100644
--- a/packages/website/src/pages/Home.tsx
+++ b/packages/website/src/pages/Home.tsx
@@ -12,7 +12,13 @@ import { Highlighter } from '../components/ui/highlighter'
 import { NeonGradientCard } from '../components/ui/neon-gradient-card'
 import { Particles } from '../components/ui/particles'
 import { SparklesText } from '../components/ui/sparkles-text'
-import { CDN_DEMO_CN_URL, CDN_DEMO_URL } from '../constants'
+import {
+	CDN_DEMO_CN_URL,
+	CDN_DEMO_URL,
+	DEMO_API_KEY,
+	DEMO_BASE_URL,
+	DEMO_MODEL,
+} from '../constants'
 
 function getInjection(useCN?: boolean) {
 	const cdn = useCN ? CDN_DEMO_CN_URL : CDN_DEMO_URL
@@ -73,13 +79,18 @@ export default function HomePage() {
 					},
 				},
 
-				// experimentalScriptExecutionTool: true,
-
-				// testing server
-				// @note: rate limit. prompt limit.
-				// model: DEMO_MODEL,
-				// baseURL: DEMO_BASE_URL,
-				// apiKey: DEMO_API_KEY,
+				model:
+					import.meta.env.DEV && import.meta.env.LLM_MODEL_NAME
+						? import.meta.env.LLM_MODEL_NAME
+						: DEMO_MODEL,
+				baseURL:
+					import.meta.env.DEV && import.meta.env.LLM_BASE_URL
+						? import.meta.env.LLM_BASE_URL
+						: DEMO_BASE_URL,
+				apiKey:
+					import.meta.env.DEV && import.meta.env.LLM_API_KEY
+						? import.meta.env.LLM_API_KEY
+						: DEMO_API_KEY,
 			})
 			win.pageAgent = pageAgent
 		}