diff --git a/Libraries/ReactNative/ReactNativeRuntimeDiagnostics.js b/Libraries/ReactNative/ReactNativeRuntimeDiagnostics.js
new file mode 100644
index 00000000000..82bea13749c
--- /dev/null
+++ b/Libraries/ReactNative/ReactNativeRuntimeDiagnostics.js
@@ -0,0 +1,68 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ */
+
+'use strict';
+
+/**
+ * Perform a set of runtime diagnostics, usually useful for test purpose.
+ * This is only meaningful for __DEV__ mode.
+ */
+export type RuntimeDiagnostics = {|
+  /**
+   * Check if the runtime diagnostics is enabled at all.
+   */
+  isEnabled: () => boolean,
+
+  /**
+   * If enabled, simulate early JavaScript errors during initialization.
+   */
+  simulateEarlyJavaScriptErrors: () => void,
+|};
+
+export type RuntimeDiagnosticFlag = 'early_js_errors' | 'all';
+
+const flags: Array<RuntimeDiagnosticFlag> = [];
+let isEnabled = false;
+let shouldEnableAll = false;
+
+if (__DEV__) {
+  if (typeof global.RN$DiagnosticFlags === 'string') {
+    global.RN$DiagnosticFlags.split(',').forEach(flag => {
+      switch (flag) {
+        case 'early_js_errors':
+        case 'all':
+          flags.push(flag);
+          break;
+        default:
+          throw Error(
+            `RuntimeDiagnosticsFlags: unknown flag was supplied: '${flag}'`,
+          );
+      }
+    });
+    isEnabled = flags.length > 0;
+    shouldEnableAll = flags.includes('all');
+  }
+}
+
+const ReactNativeRuntimeDiagnostics: RuntimeDiagnostics = {
+  isEnabled: () => isEnabled,
+  simulateEarlyJavaScriptErrors: () => {
+    if (__DEV__) {
+      if (!isEnabled) {
+        return;
+      }
+      if (shouldEnableAll || flags.includes('early_js_errors')) {
+        throw Error('[Runtime Diagnostics] Throwing a JavaScript error.');
+      }
+    }
+  },
+};
+
+module.exports = ReactNativeRuntimeDiagnostics;