diff --git a/src/settings.ts b/src/settings.ts
index 8a9dbd11..0afda0a9 100644
--- a/src/settings.ts
+++ b/src/settings.ts
@@ -107,6 +107,7 @@ interface Refs {
   se: HTMLUListElement;
   sd: HTMLUListElement;
   reset: HTMLButtonElement;
+  backup: HTMLInputElement;
 }
 
 const meta = compile(`
@@ -134,6 +135,12 @@ const meta = compile(`
       </label>
     </div>
 
+    <div class=row>
+      <label>
+        <input @backup type=checkbox class=box> Backup and sync settings
+      </label>
+    </div>
+
     <div class=row>
       <label>Sections</label>
       <fieldset>
@@ -244,6 +251,28 @@ const Settings = () => {
     }
   };
 
+  refs.backup.onchange = async () => {
+    if (refs.backup.checked) {
+      const bytesInUse = await chrome.storage.local.getBytesInUse();
+      const quotaBytes = chrome.storage.local.QUOTA_BYTES;
+      if (bytesInUse > quotaBytes) {
+        refs.feedback.textContent = `Warning: Settings exceed local storage limit. Current size: ${bytesInUse} bytes, Allowed size: ${quotaBytes} bytes, Total size over: ${bytesInUse - quotaBytes} bytes.`;
+        refs.backup.checked = false;
+      } else {
+        void chrome.storage.local.set({
+          backup: true,
+        });
+        void chrome.storage.sync.set({
+          backup: true,
+        });
+      }
+    } else {
+      void chrome.storage.local.set({
+        backup: false,
+      });
+    }
+  };
+
   // eslint-disable-next-line no-multi-assign
   refs.se.ondragover = refs.sd.ondragover = (event) => {
     event.preventDefault();
@@ -267,6 +296,7 @@ const Settings = () => {
 
   void updateTheme(themeName);
   refs.b.checked = !storage.b;
+  refs.backup.checked = !!storage.backup;
   updateOrder([orderEnabled, orderDisabled], true);
 
   return root;
diff --git a/src/sw.ts b/src/sw.ts
index 1504971f..e39bc52f 100644
--- a/src/sw.ts
+++ b/src/sw.ts
@@ -23,6 +23,13 @@ chrome.runtime.onInstalled.addListener(async () => {
     t: themes[settings.tn ?? 'auto'],
   });
 
+  // Include backup and sync setting during installation or update
+  if (settings.backupSync) {
+    void chrome.storage.local.set({
+      backupSync: settings.backupSync,
+    });
+  }
+
   // TODO: Open settings page on install?
   // if (details.reason === ('install' as chrome.runtime.OnInstalledReason.INSTALL)) {
   //   void chrome.tabs.create({
diff --git a/src/utils.ts b/src/utils.ts
index 3869d9f2..eb2a79b0 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -50,4 +50,8 @@ export const handleClick = (event: MouseEvent): false | void => {
   }
 
   s.focus();
+
+  if (storage.backupSync) {
+    void chrome.storage.sync.set(storage);
+  }
 };
diff --git a/test/unit/settings.test.ts b/test/unit/settings.test.ts
index f6967e87..e6b75ca1 100644
--- a/test/unit/settings.test.ts
+++ b/test/unit/settings.test.ts
@@ -14,7 +14,6 @@ async function load() {
     if (input === 'themes.json') {
       return Promise.resolve(new Response(themes));
     }
-    // eslint-disable-next-line @typescript-eslint/no-base-to-string
     throw new Error(`Unexpected fetch call: ${String(input)}`);
   });
   // eslint-disable-next-line no-multi-assign
@@ -62,6 +61,59 @@ test('gets stored user settings once on load', async () => {
   expect(spy).toHaveBeenCalledTimes(1);
 });
 
+test('displays warning and unchecks backup box if settings exceed local storage', async () => {
+  expect.assertions(4);
+  const spy = spyOn(chrome.storage.local, 'getBytesInUse').mockResolvedValueOnce(11000000);
+  await load();
+  const backupCheckbox = document.querySelector('input[type="checkbox"][class="box"]');
+  expect(backupCheckbox).toBeInstanceOf(HTMLInputElement);
+  if (backupCheckbox instanceof HTMLInputElement) {
+    backupCheckbox.click();
+    expect(spy).toHaveBeenCalledTimes(1);
+    expect(backupCheckbox.checked).toBeFalse();
+    const feedback = document.querySelector('div[feedback]');
+    expect(feedback?.textContent).toContain('Warning: Settings exceed local storage limit.');
+  }
+});
+
+test('syncs backup setting choice when enabled', async () => {
+  expect.assertions(2);
+  const spy = spyOn(chrome.storage.local, 'set');
+  await load();
+  const backupCheckbox = document.querySelector('input[type="checkbox"][class="box"]');
+  expect(backupCheckbox).toBeInstanceOf(HTMLInputElement);
+  if (backupCheckbox instanceof HTMLInputElement) {
+    backupCheckbox.click();
+    expect(spy).toHaveBeenCalledWith({ backup: true });
+  }
+});
+
+test('syncs settings to chrome.storage.sync when backup and sync is enabled', async () => {
+  expect.assertions(2);
+  const spy = spyOn(chrome.storage.sync, 'set');
+  await load();
+  const backupCheckbox = document.querySelector('input[type="checkbox"][class="box"]');
+  expect(backupCheckbox).toBeInstanceOf(HTMLInputElement);
+  if (backupCheckbox instanceof HTMLInputElement) {
+    backupCheckbox.click();
+    expect(spy).toHaveBeenCalledWith({ backup: true });
+  }
+});
+
+test('does not remove backed-up settings when disabling sync', async () => {
+  expect.assertions(2);
+  const spy = spyOn(chrome.storage.local, 'set');
+  await load();
+  const backupCheckbox = document.querySelector('input[type="checkbox"][class="box"]');
+  expect(backupCheckbox).toBeInstanceOf(HTMLInputElement);
+  if (backupCheckbox instanceof HTMLInputElement) {
+    backupCheckbox.click(); // Enable sync
+    backupCheckbox.click(); // Disable sync
+    expect(spy).toHaveBeenCalledWith({ backup: true });
+    expect(spy).toHaveBeenCalledWith({ backup: false });
+  }
+});
+
 const css = await Bun.file('dist/settings.css').text();
 
 describe('CSS', () => {
@@ -92,12 +144,12 @@ describe('CSS', () => {
 
   test('does not contain ":root"', () => {
     expect.assertions(1);
-    expect(css).not.toInclude(':root');
+    expect(css).not toInclude(':root');
   });
 
   test('compiled AST is not empty', () => {
     expect.assertions(1);
-    expect(ast).not.toBeEmpty();
+    expect(ast).not toBeEmpty();
   });
 
   test('does not have any rules with a ":root" selector', () => {