diff --git a/app/lib/hooks/pingTelemetry.ts b/app/lib/hooks/pingTelemetry.ts
index 21f8bf01..94427e40 100644
--- a/app/lib/hooks/pingTelemetry.ts
+++ b/app/lib/hooks/pingTelemetry.ts
@@ -1,5 +1,11 @@
 // FIXME ping telemetry server directly instead of going through the backend.
 
+let gDisableTelemetry = false;
+
+export function disableTelemetry() {
+  gDisableTelemetry = true;
+}
+
 // We do this to work around CORS insanity.
 export async function pingTelemetry(event: string, data: any) {
   const requestBody: any = {
@@ -26,6 +32,10 @@ export class ChatMessageTelemetry {
   }
 
   private _ping(event: string, data: any = {}) {
+    if (gDisableTelemetry) {
+      return;
+    }
+
     pingTelemetry(event, {
       ...data,
       messageId: this.id,
diff --git a/app/lib/persistence/message.ts b/app/lib/persistence/message.ts
index 68c1c21d..59fa8041 100644
--- a/app/lib/persistence/message.ts
+++ b/app/lib/persistence/message.ts
@@ -9,8 +9,10 @@ interface MessageBase {
   id: string;
   role: MessageRole;
   repositoryId?: string;
+  repositoryURL?: string;
   peanuts?: number;
   category?: string;
+  createTime?: string;
 
   // Not part of the protocol, indicates whether the user has explicitly approved
   // the message. Once approved, the approve/reject UI is not shown again for the message.
diff --git a/app/lib/replay/ChatManager.ts b/app/lib/replay/ChatManager.ts
index c71df69a..4d761004 100644
--- a/app/lib/replay/ChatManager.ts
+++ b/app/lib/replay/ChatManager.ts
@@ -12,6 +12,7 @@ import { chatStore } from '~/lib/stores/chat';
 import { debounce } from '~/utils/debounce';
 import { getSupabase } from '~/lib/supabase/client';
 import { pingTelemetry } from '~/lib/hooks/pingTelemetry';
+import { sendChatMessageMocked, usingMockChat } from './MockChat';
 
 // We report to telemetry if we start a message and don't get any response
 // before this timeout.
@@ -367,6 +368,11 @@ export async function sendChatMessage(
   references: ChatReference[],
   callbacks: ChatMessageCallbacks,
 ) {
+  if (usingMockChat()) {
+    await sendChatMessageMocked(callbacks);
+    return;
+  }
+
   if (gMessageChatManager) {
     gMessageChatManager.destroy();
   }
diff --git a/app/lib/replay/MockChat.ts b/app/lib/replay/MockChat.ts
new file mode 100644
index 00000000..2f75ad0a
--- /dev/null
+++ b/app/lib/replay/MockChat.ts
@@ -0,0 +1,46 @@
+/*
+ * Mock chats generate a hardcoded series of responses to a chat message.
+ * This avoids non-deterministic behavior in the chat backend and is helpful for
+ * development, testing, demos etc.
+ */
+
+import { assert, waitForTime } from '~/lib/replay/ReplayProtocolClient';
+import type { Message } from '~/lib/persistence/message';
+import type { ChatMessageCallbacks } from './ChatManager';
+import { disableTelemetry } from '~/lib/hooks/pingTelemetry';
+
+// Add your mock chat messages here!
+const gMockChat: Message[] | undefined = undefined;
+
+if (gMockChat) {
+  disableTelemetry();
+}
+
+export function usingMockChat() {
+  return !!gMockChat;
+}
+
+export async function sendChatMessageMocked(callbacks: ChatMessageCallbacks) {
+  assert(gMockChat, 'Mock chat is not defined');
+
+  console.log('Using mock chat', gMockChat);
+
+  assert(gMockChat[0].createTime, 'Mock chat first message must have a create time');
+  let currentTime = Date.parse(gMockChat[0].createTime);
+
+  for (const message of gMockChat) {
+    if (message.role === 'user') {
+      continue;
+    }
+
+    if (message.createTime) {
+      const messageTime = Date.parse(message.createTime);
+      if (messageTime > currentTime) {
+        await waitForTime(messageTime - currentTime);
+        currentTime = messageTime;
+      }
+    }
+
+    callbacks.onResponsePart(message);
+  }
+}
diff --git a/app/lib/replay/ReplayProtocolClient.ts b/app/lib/replay/ReplayProtocolClient.ts
index 382ff8ce..f3771894 100644
--- a/app/lib/replay/ReplayProtocolClient.ts
+++ b/app/lib/replay/ReplayProtocolClient.ts
@@ -26,6 +26,10 @@ export function defer<T>(): { promise: Promise<T>; resolve: (value: T) => void;
   return { promise, resolve: resolve!, reject: reject! };
 }
 
+export function waitForTime(ms: number) {
+  return new Promise((resolve) => setTimeout(resolve, ms));
+}
+
 export function uint8ArrayToBase64(data: Uint8Array) {
   let str = '';