diff --git a/ui/src/ui/uuid.test.ts b/ui/src/ui/uuid.test.ts
index 9f7ccbf81..2d5421bdd 100644
--- a/ui/src/ui/uuid.test.ts
+++ b/ui/src/ui/uuid.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 
 import { generateUUID } from "./uuid";
 
@@ -26,7 +26,13 @@ describe("generateUUID", () => {
   });
 
   it("still returns a v4 UUID when crypto is missing", () => {
-    const id = generateUUID(null);
-    expect(id).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/);
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    try {
+      const id = generateUUID(null);
+      expect(id).toMatch(/^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/);
+      expect(warnSpy).toHaveBeenCalled();
+    } finally {
+      warnSpy.mockRestore();
+    }
   });
 });
diff --git a/ui/src/ui/uuid.ts b/ui/src/ui/uuid.ts
index f231d0f7f..7c927cda1 100644
--- a/ui/src/ui/uuid.ts
+++ b/ui/src/ui/uuid.ts
@@ -3,6 +3,8 @@ export type CryptoLike = {
   getRandomValues?: ((array: Uint8Array) => Uint8Array) | undefined;
 };
 
+let warnedWeakCrypto = false;
+
 function uuidFromBytes(bytes: Uint8Array): string {
   bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
   bytes[8] = (bytes[8] & 0x3f) | 0x80; // variant 1
@@ -29,6 +31,12 @@ function weakRandomBytes(): Uint8Array {
   return bytes;
 }
 
+function warnWeakCryptoOnce() {
+  if (warnedWeakCrypto) return;
+  warnedWeakCrypto = true;
+  console.warn("[uuid] crypto API missing; falling back to weak randomness");
+}
+
 export function generateUUID(cryptoLike: CryptoLike | null = globalThis.crypto): string {
   if (cryptoLike && typeof cryptoLike.randomUUID === "function") return cryptoLike.randomUUID();
 
@@ -38,5 +46,6 @@ export function generateUUID(cryptoLike: CryptoLike | null = globalThis.crypto):
     return uuidFromBytes(bytes);
   }
 
+  warnWeakCryptoOnce();
   return uuidFromBytes(weakRandomBytes());
 }