diff --git a/src/components/MethodInvoker.tsx b/src/components/MethodInvoker.tsx
index 2655bcb..9ecc379 100644
--- a/src/components/MethodInvoker.tsx
+++ b/src/components/MethodInvoker.tsx
@@ -8,6 +8,7 @@ import { fromCurl, rpcParams, toCurl } from '../lib/curl';
 import { formatBytes, formatDuration, jsonByteSize } from '../lib/format';
 import { createRequest, type JsonRpcParams, type JsonRpcRequest } from '../lib/rpc';
 import type { JsonSchema } from '../lib/smdToJsonSchema';
+import { randomUUID } from '../lib/uuid';
 import { useStore } from '../store/store';
 import { FormFromSchema } from './FormFromSchema';
 import { JsonViewer } from './JsonViewer';
@@ -65,7 +66,7 @@ export function MethodInvoker({ schema, method, endpoint, headers }: MethodInvok
           setMeta({ durationMs: performance.now() - startedAtRef.current, size: jsonByteSize(resp) });
           setLastResult({ value: resp.error ?? resp.result, errored: Boolean(resp.error) });
           addHistory({
-            id: crypto.randomUUID(),
+            id: randomUUID(),
             method,
             params,
             response: resp.result,
@@ -77,7 +78,7 @@ export function MethodInvoker({ schema, method, endpoint, headers }: MethodInvok
         onError: (err) => {
           if (isAbort(err)) return;
           addHistory({
-            id: crypto.randomUUID(),
+            id: randomUUID(),
             method,
             params,
             error: { message: String(err) },
diff --git a/src/lib/__tests__/uuid.test.ts b/src/lib/__tests__/uuid.test.ts
new file mode 100644
index 0000000..d6ab246
--- /dev/null
+++ b/src/lib/__tests__/uuid.test.ts
@@ -0,0 +1,27 @@
+import { describe, it, expect, afterEach } from 'vitest';
+
+import { randomUUID } from '../uuid';
+
+const V4 = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
+
+describe('randomUUID', () => {
+  const original = crypto.randomUUID;
+
+  afterEach(() => {
+    Object.defineProperty(crypto, 'randomUUID', { value: original, configurable: true, writable: true });
+  });
+
+  it('returns a valid RFC 4122 v4 UUID', () => {
+    expect(randomUUID()).toMatch(V4);
+  });
+
+  it('returns unique values', () => {
+    expect(randomUUID()).not.toBe(randomUUID());
+  });
+
+  it('falls back to getRandomValues when crypto.randomUUID is unavailable (insecure context)', () => {
+    // Simulate a non-secure context (plain HTTP) where randomUUID is missing.
+    Object.defineProperty(crypto, 'randomUUID', { value: undefined, configurable: true, writable: true });
+    expect(randomUUID()).toMatch(V4);
+  });
+});
diff --git a/src/lib/rpc.ts b/src/lib/rpc.ts
index 0bb3ea3..7eef5ba 100644
--- a/src/lib/rpc.ts
+++ b/src/lib/rpc.ts
@@ -4,6 +4,8 @@
  * adding a request timeout and cancellation (see UX_AUDIT.md 3.8).
  */
 
+import { randomUUID } from './uuid';
+
 export type JsonRpcParams = Record<string, unknown> | unknown[];
 
 export interface JsonRpcRequest {
@@ -28,7 +30,7 @@ export interface JsonRpcResponse<T = unknown> {
 
 /** Builds a JSON-RPC 2.0 request envelope with a fresh id. */
 export function createRequest(method: string, params: JsonRpcParams = {}): JsonRpcRequest {
-  return { id: crypto.randomUUID(), jsonrpc: '2.0', method, params };
+  return { id: randomUUID(), jsonrpc: '2.0', method, params };
 }
 
 /** Request headers with the JSON content type applied. */
diff --git a/src/lib/uuid.ts b/src/lib/uuid.ts
new file mode 100644
index 0000000..6f8283f
--- /dev/null
+++ b/src/lib/uuid.ts
@@ -0,0 +1,25 @@
+/**
+ * Returns an RFC 4122 version 4 UUID.
+ *
+ * `crypto.randomUUID()` is only exposed in secure contexts (HTTPS or
+ * `http://localhost`). SMDBox is frequently served over plain HTTP on an IP
+ * address (e.g. straight from a JSON-RPC backend during development), where
+ * `crypto.randomUUID` is `undefined` and calling it throws
+ * `TypeError: crypto.randomUUID is not a function`, crashing the app.
+ *
+ * `crypto.getRandomValues()` is available in insecure contexts too, so we fall
+ * back to it when `randomUUID` is missing.
+ */
+export function randomUUID(): string {
+  if (typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function') {
+    return crypto.randomUUID();
+  }
+
+  const bytes = crypto.getRandomValues(new Uint8Array(16));
+  const at = (i: number): number => bytes[i] ?? 0;
+  bytes[6] = (at(6) & 0x0f) | 0x40; // version 4
+  bytes[8] = (at(8) & 0x3f) | 0x80; // variant 10xx
+
+  const hex = Array.from(bytes, (b) => b.toString(16).padStart(2, '0')).join('');
+  return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20)}`;
+}
diff --git a/src/store/store.ts b/src/store/store.ts
index 30918cf..512ba58 100644
--- a/src/store/store.ts
+++ b/src/store/store.ts
@@ -2,6 +2,7 @@ import { create } from 'zustand';
 
 import { writeState } from '../lib/persist';
 import type { JsonRpcParams } from '../lib/rpc';
+import { randomUUID } from '../lib/uuid';
 
 // Soft cap to keep IndexedDB bounded; the old hard limit of 10 is gone.
 const HISTORY_LIMIT = 500;
@@ -224,7 +225,7 @@ export const useStore = create<AppState>((set) => ({
 
   saveRequest: (name, method, params) =>
     set((s) => ({
-      saved: [...s.saved, { id: crypto.randomUUID(), name, method, params, ts: Date.now() }],
+      saved: [...s.saved, { id: randomUUID(), name, method, params, ts: Date.now() }],
     })),
 
   deleteSaved: (id) => set((s) => ({ saved: s.saved.filter((r) => r.id !== id) })),
@@ -249,7 +250,7 @@ export const useStore = create<AppState>((set) => ({
     set((s) => ({
       savedResponses: [
         ...s.savedResponses,
-        { id: crypto.randomUUID(), name, method, response, ts: Date.now() },
+        { id: randomUUID(), name, method, response, ts: Date.now() },
       ],
     })),
 
@@ -308,7 +309,7 @@ export const useStore = create<AppState>((set) => ({
           activeEnvironmentId: existing.id,
         };
       }
-      const id = crypto.randomUUID();
+      const id = randomUUID();
       return {
         environments: [...s.environments, { id, name: trimmed, ...snapshot }],
         activeEnvironmentId: id,