diff --git a/apps/webclaw/src/components/attachment-button.tsx b/apps/webclaw/src/components/attachment-button.tsx
index aca2ddb..128ba22 100644
--- a/apps/webclaw/src/components/attachment-button.tsx
+++ b/apps/webclaw/src/components/attachment-button.tsx
@@ -5,7 +5,7 @@ import { HugeiconsIcon } from '@hugeicons/react'
 import { PlusSignIcon } from '@hugeicons/core-free-icons'
 
 import { Button } from '@/components/ui/button'
-import { cn } from '@/lib/utils'
+import { cn, randomUUID } from '@/lib/utils'
 
 /** Maximum file size before compression (10MB) */
 const MAX_FILE_SIZE = 10 * 1024 * 1024
@@ -202,7 +202,7 @@ export function AttachmentButton({
       // Reset input to allow selecting the same file again
       event.target.value = ''
 
-      const id = crypto.randomUUID()
+      const id = randomUUID()
 
       // Validate file type
       if (!isAcceptedImage(file)) {
diff --git a/apps/webclaw/src/lib/utils.ts b/apps/webclaw/src/lib/utils.ts
index 914ec86..0bed9a8 100644
--- a/apps/webclaw/src/lib/utils.ts
+++ b/apps/webclaw/src/lib/utils.ts
@@ -5,3 +5,23 @@ import type { ClassValue } from 'clsx'
 export function cn(...inputs: Array<ClassValue>) {
   return twMerge(clsx(inputs))
 }
+
+export function randomUUID() {
+  // Check if we're in a secure context with crypto.randomUUID available
+  if (
+    typeof window !== 'undefined' &&
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+    window.crypto &&
+    // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+    window.crypto.randomUUID
+  ) {
+    return window.crypto.randomUUID()
+  }
+
+  // Fallback for insecure contexts (e.g. HTTP on LAN)
+  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
+    const r = (Math.random() * 16) | 0
+    const v = c === 'x' ? r : (r & 0x3) | 0x8
+    return v.toString(16)
+  })
+}
diff --git a/apps/webclaw/src/screens/chat/chat-screen-utils.ts b/apps/webclaw/src/screens/chat/chat-screen-utils.ts
index 59c7b99..f884713 100644
--- a/apps/webclaw/src/screens/chat/chat-screen-utils.ts
+++ b/apps/webclaw/src/screens/chat/chat-screen-utils.ts
@@ -1,5 +1,6 @@
 import type { GatewayMessage } from './types'
 import type { AttachmentFile } from '@/components/attachment-button'
+import { randomUUID } from '@/lib/utils'
 
 type OptimisticMessagePayload = {
   clientId: string
@@ -11,7 +12,7 @@ export function createOptimisticMessage(
   body: string,
   attachments?: Array<AttachmentFile>,
 ): OptimisticMessagePayload {
-  const clientId = crypto.randomUUID()
+  const clientId = randomUUID()
   const optimisticId = `opt-${clientId}`
   const timestamp = Date.now()
 
diff --git a/apps/webclaw/src/screens/chat/chat-screen.tsx b/apps/webclaw/src/screens/chat/chat-screen.tsx
index f1774b5..387f907 100644
--- a/apps/webclaw/src/screens/chat/chat-screen.tsx
+++ b/apps/webclaw/src/screens/chat/chat-screen.tsx
@@ -44,7 +44,7 @@ import type { AttachmentFile } from '@/components/attachment-button'
 import type { ChatComposerHelpers } from './components/chat-composer'
 import { useExport } from '@/hooks/use-export'
 import { useChatSettings } from '@/hooks/use-chat-settings'
-import { cn } from '@/lib/utils'
+import { cn, randomUUID } from '@/lib/utils'
 
 type ChatScreenProps = {
   activeFriendlyId: string
@@ -270,7 +270,7 @@ export function ChatScreen({
         friendlyId,
         message: body,
         thinking: settings.thinkingLevel,
-        idempotencyKey: crypto.randomUUID(),
+        idempotencyKey: randomUUID(),
         attachments: attachmentsPayload,
       }),
     })