diff --git a/index.html b/index.html
index 4ffca621..5f0c72f6 100644
--- a/index.html
+++ b/index.html
@@ -56,6 +56,9 @@
   <body>
     <noscript>You need to enable JavaScript to run this app.</noscript>
     <div id="root"></div>
+    <script>
+      window.__CONNECT_BUNDLE_LOAD_STARTED_AT__ = performance.now();
+    </script>
     <script type="module" src="/src/index.jsx"></script>
 
     <script async src="https://www.googletagmanager.com/gtag/js?id=G-SD0LELN29K"></script>
diff --git a/src/App.jsx b/src/App.jsx
index faed1727..27936c49 100644
--- a/src/App.jsx
+++ b/src/App.jsx
@@ -1,4 +1,4 @@
-import React, { Component, lazy, Suspense } from 'react';
+import React, { Component, lazy } from 'react';
 import { Provider } from 'react-redux';
 import { Route, Switch, Redirect } from 'react-router';
 import { ConnectedRouter } from 'connected-react-router';
@@ -14,6 +14,7 @@ import { fetchTurnCredentials } from './utils/turn';
 import store, { history } from './store';
 
 import ErrorFallback from './components/ErrorFallback';
+import BundleLoadBoundary from './components/BundleLoadBoundary';
 import FullPageLoading from './components/FullPageLoading';
 
 const Explorer = lazy(() => import('./components/explorer'));
@@ -123,11 +124,7 @@ class App extends Component {
     }
 
     const showLogin = !MyCommaAuth.isAuthenticated() && !getZoom(window.location.pathname) && !getSegmentRange(window.location.pathname);
-    let content = (
-      <Suspense fallback={<FullPageLoading />}>
-        { showLogin ? this.anonymousRoutes() : this.authRoutes() }
-      </Suspense>
-    );
+    let content = showLogin ? this.anonymousRoutes() : this.authRoutes();
 
     // Use ErrorBoundary in production only
     if (import.meta.env.PROD) {
@@ -141,7 +138,11 @@ class App extends Component {
     return (
       <Provider store={store}>
         <ConnectedRouter history={history}>
-          {content}
+          <Route render={({ location }) => (
+            <BundleLoadBoundary key={location.key || location.pathname}>
+              {content}
+            </BundleLoadBoundary>
+          )} />
         </ConnectedRouter>
       </Provider>
     );
diff --git a/src/components/AppHeader/AccountMenu.jsx b/src/components/AppHeader/AccountMenu.jsx
index af0d4174..48dba215 100644
--- a/src/components/AppHeader/AccountMenu.jsx
+++ b/src/components/AppHeader/AccountMenu.jsx
@@ -1,9 +1,11 @@
-import React, { useCallback, useMemo } from 'react';
+import React, { useCallback, useMemo, useState } from 'react';
 import dayjs from 'dayjs';
+import { Switch } from '@material-ui/core';
 
 import MyCommaAuth from '@commaai/my-comma-auth';
 
 import { USERADMIN_URL_ROOT } from '../../api';
+import { getDeveloperToolsEnabled, setDeveloperToolsEnabled } from '../../userSettings';
 
 const logOut = async () => {
   await MyCommaAuth.logOut();
@@ -35,12 +37,19 @@ const Version = () => {
 
 const AccountMenu = ({ profile, open, onClose }) => {
   const version = useMemo(() => <Version />, []);
+  const [developerToolsEnabled, setDeveloperToolsState] = useState(getDeveloperToolsEnabled);
 
   const onLogOut = useCallback(() => {
     onClose();
     logOut();
   }, [onClose]);
 
+  const onDeveloperToolsChange = useCallback((event) => {
+    const enabled = event.target.checked;
+    setDeveloperToolsState(enabled);
+    setDeveloperToolsEnabled(enabled);
+  }, []);
+
   if (!open) {
     return null;
   }
@@ -64,6 +73,15 @@ const AccountMenu = ({ profile, open, onClose }) => {
         >
           Manage Account
         </a>
+        <label className="flex w-full cursor-pointer items-center justify-between px-4 py-2 text-white hover:bg-white/10">
+          <span>Developer tools</span>
+          <Switch
+            checked={developerToolsEnabled}
+            color="primary"
+            inputProps={{ 'aria-label': 'Enable developer tools' }}
+            onChange={onDeveloperToolsChange}
+          />
+        </label>
         <button
           className="block w-full px-4 py-3 text-left text-white hover:bg-white/10"
           onClick={onLogOut}
diff --git a/src/components/BundleLoadBoundary/index.jsx b/src/components/BundleLoadBoundary/index.jsx
new file mode 100644
index 00000000..849be31d
--- /dev/null
+++ b/src/components/BundleLoadBoundary/index.jsx
@@ -0,0 +1,108 @@
+import React, { Component, Suspense } from 'react';
+import PropTypes from 'prop-types';
+import { DEV_TOOLS_CHANGED_EVENT, getDeveloperToolsEnabled } from '../../userSettings';
+import FullPageLoading from '../FullPageLoading';
+
+let initialLoadClaimed = false;
+
+const now = () => (
+  typeof performance !== 'undefined' && typeof performance.now === 'function'
+    ? performance.now()
+    : Date.now()
+);
+
+const getLoadStart = () => {
+  if (!initialLoadClaimed) {
+    initialLoadClaimed = true;
+    if (typeof window !== 'undefined' && Number.isFinite(window.__CONNECT_BUNDLE_LOAD_STARTED_AT__)) {
+      return window.__CONNECT_BUNDLE_LOAD_STARTED_AT__;
+    }
+  }
+  return now();
+};
+
+class ReadyMarker extends Component {
+  componentDidMount() {
+    this.props.onReady();
+  }
+
+  render() {
+    return null;
+  }
+}
+
+ReadyMarker.propTypes = {
+  onReady: PropTypes.func.isRequired,
+};
+
+class BundleLoadBoundary extends Component {
+  constructor(props) {
+    super(props);
+    this.startedAt = getLoadStart();
+    this.animationFrame = null;
+    this.state = {
+      developerToolsEnabled: getDeveloperToolsEnabled(),
+      durationMs: null,
+    };
+    this.handleReady = this.handleReady.bind(this);
+    this.handleDeveloperToolsChanged = this.handleDeveloperToolsChanged.bind(this);
+  }
+
+  componentDidMount() {
+    window.addEventListener(DEV_TOOLS_CHANGED_EVENT, this.handleDeveloperToolsChanged);
+  }
+
+  componentWillUnmount() {
+    window.removeEventListener(DEV_TOOLS_CHANGED_EVENT, this.handleDeveloperToolsChanged);
+    if (this.animationFrame !== null && typeof cancelAnimationFrame === 'function') {
+      cancelAnimationFrame(this.animationFrame);
+    }
+  }
+
+  handleDeveloperToolsChanged(event) {
+    this.setState({ developerToolsEnabled: event.detail.enabled });
+  }
+
+  handleReady() {
+    const finish = () => {
+      this.animationFrame = null;
+      this.setState({ durationMs: Math.max(0, Math.round(now() - this.startedAt)) });
+    };
+
+    if (typeof requestAnimationFrame === 'function') {
+      this.animationFrame = requestAnimationFrame(finish);
+    } else {
+      finish();
+    }
+  }
+
+  render() {
+    const { children } = this.props;
+    const { developerToolsEnabled, durationMs } = this.state;
+
+    return (
+      <>
+        <Suspense fallback={<FullPageLoading />}>
+          {children}
+          <ReadyMarker onReady={this.handleReady} />
+        </Suspense>
+        {durationMs === null
+          ? <FullPageLoading />
+          : developerToolsEnabled && (
+            <footer
+              className="pointer-events-none fixed inset-x-0 bottom-0 z-[1300] border-t border-white/10 bg-[#16181A]/[.92] px-3 py-1 text-right text-[11px] leading-4 text-white/50"
+              data-testid="bundle-load-footer"
+            >
+              Bundle loaded in {durationMs} ms
+            </footer>
+          )}
+      </>
+    );
+  }
+}
+
+BundleLoadBoundary.propTypes = {
+  children: PropTypes.node.isRequired,
+};
+
+export default BundleLoadBoundary;
diff --git a/src/userSettings.js b/src/userSettings.js
new file mode 100644
index 00000000..9c13c4e0
--- /dev/null
+++ b/src/userSettings.js
@@ -0,0 +1,24 @@
+const DEV_TOOLS_STORAGE_KEY = 'developerToolsEnabled';
+export const DEV_TOOLS_CHANGED_EVENT = 'connect:developer-tools-changed';
+
+export const getDeveloperToolsEnabled = () => {
+  try {
+    return window.localStorage.getItem(DEV_TOOLS_STORAGE_KEY) === 'true';
+  } catch {
+    return false;
+  }
+};
+
+export const setDeveloperToolsEnabled = (enabled) => {
+  const nextValue = Boolean(enabled);
+
+  try {
+    window.localStorage.setItem(DEV_TOOLS_STORAGE_KEY, String(nextValue));
+  } catch {
+    // Keep the setting usable for this session when storage is unavailable.
+  }
+
+  window.dispatchEvent(new CustomEvent(DEV_TOOLS_CHANGED_EVENT, {
+    detail: { enabled: nextValue },
+  }));
+};
