diff --git a/src/static/css/timeslider.css b/src/static/css/timeslider.css
index 252248b339a..65506021ec0 100644
--- a/src/static/css/timeslider.css
+++ b/src/static/css/timeslider.css
@@ -120,15 +120,33 @@
   overflow-y: auto;
 }
 #outerdocbody {
-  display: block;
+  display: flex;
+  flex-direction: row;
+  justify-content: center;
+  align-items: flex-start;
   width: 100%;
 }
 
+#outerdocbody > #sidediv {
+  flex: 0 0 auto;
+  padding-top: 30px;
+  padding-bottom: 30px;
+}
+
+#outerdocbody > #innerdocbody {
+  flex: 1 1 auto;
+  min-width: 0;
+  padding-right: calc(var(--editor-horizontal-padding, 0px) + 15px);
+  padding-top: 30px;
+  padding-left: calc(var(--editor-horizontal-padding, 0px) + 15px);
+  padding-bottom: 30px;
+}
+
 #innerdocbody {
   white-space: normal;
   word-break: break-word;
   width: 100%;
-  margin: 0 auto;
+  margin: 0;
   height: auto;
 }
 
@@ -151,4 +169,4 @@
     display: flex;
     flex-wrap: wrap;
   }
-}
\ No newline at end of file
+}
diff --git a/src/static/js/broadcast.ts b/src/static/js/broadcast.ts
index 01e4a2edf01..37d98a6e8aa 100644
--- a/src/static/js/broadcast.ts
+++ b/src/static/js/broadcast.ts
@@ -132,6 +132,72 @@ const loadBroadcastJS = (socket, sendSocketMsg, fireWhenAllScriptsAreLoaded, Bro
     },
   };
 
+  const targetBody = document.getElementById('innerdocbody');
+  const sideDiv = document.getElementById('sidediv');
+  const sideDivInner = document.getElementById('sidedivinner');
+  const appendNewSideDivLine = () => {
+    const lineDiv = document.createElement('div');
+    sideDivInner.appendChild(lineDiv);
+    const lineSpan = document.createElement('span');
+    lineSpan.classList.add('line-number');
+    lineSpan.appendChild(document.createTextNode(sideDivInner.children.length));
+    lineDiv.appendChild(lineSpan);
+  };
+
+  const updateLineNumbers = () => {
+    if (!targetBody || !sideDiv || !sideDivInner) return;
+    const lineOffsets = [];
+    const lineHeights = [];
+    const innerdocbodyStyles = getComputedStyle(targetBody);
+    const defaultLineHeight = parseInt(innerdocbodyStyles.lineHeight);
+
+    for (const docLine of targetBody.children) {
+      let height;
+      const nextDocLine = docLine.nextElementSibling;
+      if (nextDocLine) {
+        if (lineOffsets.length === 0) {
+          height = nextDocLine.offsetTop - parseInt(
+              innerdocbodyStyles.getPropertyValue('padding-top'));
+        } else {
+          height = nextDocLine.offsetTop - docLine.offsetTop;
+        }
+      } else {
+        height = docLine.clientHeight || docLine.offsetHeight;
+      }
+      lineOffsets.push(height);
+
+      if (docLine.clientHeight !== defaultLineHeight && docLine.firstElementChild != null) {
+        const elementStyle = window.getComputedStyle(docLine.firstElementChild);
+        const lineHeight = parseInt(elementStyle.getPropertyValue('line-height'));
+        const marginBottom = parseInt(elementStyle.getPropertyValue('margin-bottom'));
+        lineHeights.push(lineHeight + marginBottom);
+      } else {
+        lineHeights.push(defaultLineHeight);
+      }
+    }
+
+    const newNumLines = Math.max(targetBody.children.length, 1);
+    while (sideDivInner.children.length < newNumLines) appendNewSideDivLine();
+    while (sideDivInner.children.length > newNumLines) sideDivInner.lastElementChild.remove();
+    for (const [i, sideDivLine] of Array.prototype.entries.call(sideDivInner.children)) {
+      sideDivLine.style.height = `${lineOffsets[i]}px`;
+      sideDivLine.style.lineHeight = `${lineHeights[i]}px`;
+    }
+    $(sideDiv).addClass('sidedivdelayed');
+  };
+
+  let lineNumberUpdatePending = false;
+  const scheduleLineNumberUpdate = () => {
+    if (lineNumberUpdatePending) return;
+    lineNumberUpdatePending = true;
+    window.requestAnimationFrame(() => {
+      window.requestAnimationFrame(() => {
+        lineNumberUpdatePending = false;
+        updateLineNumbers();
+      });
+    });
+  };
+
   const applyChangeset = (changeset, revision, preventSliderMovement, timeDelta) => {
     // disable the next 'gotorevision' call handled by a timeslider update
     if (!preventSliderMovement) {
@@ -194,6 +260,7 @@ const loadBroadcastJS = (socket, sendSocketMsg, fireWhenAllScriptsAreLoaded, Bro
 
     padContents.currentRevision = revision;
     padContents.currentTime += timeDelta;
+    scheduleLineNumberUpdate();
 
     updateTimer();
 
@@ -465,6 +532,12 @@ const loadBroadcastJS = (socket, sendSocketMsg, fireWhenAllScriptsAreLoaded, Bro
       padContents.currentDivs.push(div);
       $('#innerdocbody').append(div);
     }
+    updateLineNumbers();
+    scheduleLineNumberUpdate();
+    $(window).on('resize', scheduleLineNumberUpdate);
+    window.addEventListener('load', scheduleLineNumberUpdate, {once: true});
+    document.fonts?.ready?.then(scheduleLineNumberUpdate);
+    $('#viewfontmenu').on('change', () => window.setTimeout(scheduleLineNumberUpdate, 0));
   });
 
   // this is necessary to keep infinite loops of events firing,
diff --git a/src/static/js/timeslider.ts b/src/static/js/timeslider.ts
index f065aee4112..d0e45973f96 100644
--- a/src/static/js/timeslider.ts
+++ b/src/static/js/timeslider.ts
@@ -36,6 +36,37 @@ let token, padId, exportLinks, socket, changesetLoader, BroadcastSlider;
 let cp = '';
 const playbackSpeedCookie = 'timesliderPlaybackSpeed';
 
+const getPrefsCookieName = () => `${cp}${window.location.protocol === 'https:' ? 'prefs' : 'prefsHttp'}`;
+
+const readPadPrefs = () => {
+  try {
+    let json = Cookies.get(getPrefsCookieName());
+    if (json == null) {
+      const unprefixed = window.location.protocol === 'https:' ? 'prefs' : 'prefsHttp';
+      if (unprefixed !== getPrefsCookieName()) json = Cookies.get(unprefixed);
+    }
+    return json == null ? {} : JSON.parse(json);
+  } catch (err) {
+    return {};
+  }
+};
+
+const writePadPrefs = (prefs) => {
+  Cookies.set(getPrefsCookieName(), JSON.stringify(prefs), {expires: 365 * 100});
+};
+
+const setPadPref = (prefName, value) => {
+  const prefs = readPadPrefs();
+  prefs[prefName] = value;
+  writePadPrefs(prefs);
+};
+
+const applyShowLineNumbers = (showLineNumbers) => {
+  padutils.setCheckbox($('#options-linenoscheck'), showLineNumbers);
+  $('body').toggleClass('line-numbers-hidden', !showLineNumbers);
+  window.requestAnimationFrame(() => $(window).trigger('resize'));
+};
+
 const init = () => {
   padutils.setupGlobalExceptionHandler();
   $(document).ready(() => {
@@ -113,7 +144,7 @@ const fireWhenAllScriptsAreLoaded = [];
 const handleClientVars = (message) => {
   // save the client Vars
   window.clientVars = message.data;
-  cp = window.clientVars.cookiePrefix || '';
+  cp = (window as any).clientVars?.cookiePrefix || '';
 
   if (window.clientVars.sessionRefreshInterval) {
     const ping =
@@ -169,6 +200,12 @@ const handleClientVars = (message) => {
   $('#playpause_button_icon').attr('title', html10n.get('timeslider.playPause'));
   $('#leftstep').attr('title', html10n.get('timeslider.backRevision'));
   $('#rightstep').attr('title', html10n.get('timeslider.forwardRevision'));
+  padutils.bindCheckboxChange($('#options-linenoscheck'), () => {
+    const showLineNumbers = padutils.getCheckbox('#options-linenoscheck');
+    setPadPref('showLineNumbers', showLineNumbers);
+    applyShowLineNumbers(showLineNumbers);
+  });
+  applyShowLineNumbers(readPadPrefs().showLineNumbers !== false);
 
   // font family change
   $('#viewfontmenu').on('change', function () {
diff --git a/src/static/skins/colibris/timeslider.css b/src/static/skins/colibris/timeslider.css
index 263e0e592a7..dc52de73c34 100644
--- a/src/static/skins/colibris/timeslider.css
+++ b/src/static/skins/colibris/timeslider.css
@@ -82,6 +82,16 @@
   font-size: .9em;
 }
 
+.timeslider #outerdocbody > #sidediv {
+  padding-top: 30px;
+  padding-bottom: 30px;
+}
+
+.timeslider #outerdocbody > #innerdocbody {
+  padding-top: 30px;
+  padding-bottom: 30px;
+}
+
 @media (max-width: 800px) {
 
   #slider-btn-container {
@@ -95,4 +105,4 @@
   #slider-btn-container #playpause_button_icon:before {
     font-size: 18px;
   }
-}
\ No newline at end of file
+}
diff --git a/src/templates/timeslider.html b/src/templates/timeslider.html
index 08fa3e4b443..393c1255a87 100644
--- a/src/templates/timeslider.html
+++ b/src/templates/timeslider.html
@@ -110,8 +110,12 @@ <h1 class="timeslider-title">
     <!----------------------------->
 
     <div id="outerdocbody">
+      <div id="sidediv" class="sidediv">
+        <div id="sidedivinner" class="sidedivinner"></div>
+      </div>
       <div id="innerdocbody">
       </div>
+      <div id="linemetricsdiv">x</div>
     </div>
 
 
@@ -248,6 +252,10 @@ <h1 data-l10n-id="pad.settings.padSettings"></h1>
           <option value="1000" data-l10n-id="timeslider.settings.playbackSpeed.1000ms">1000 ms</option>
         </select>
       </p>
+      <p>
+        <input type="checkbox" id="options-linenoscheck">
+        <label for="options-linenoscheck" data-l10n-id="pad.settings.linenocheck"></label>
+      </p>
     </div></div>
   </div>
 </body>
diff --git a/src/tests/frontend-new/specs/timeslider_line_numbers.spec.ts b/src/tests/frontend-new/specs/timeslider_line_numbers.spec.ts
new file mode 100644
index 00000000000..86037269961
--- /dev/null
+++ b/src/tests/frontend-new/specs/timeslider_line_numbers.spec.ts
@@ -0,0 +1,72 @@
+import {expect, test} from "@playwright/test";
+import {clearPadContent, goToNewPad, writeToPad} from "../helper/padHelper";
+import {showSettings} from "../helper/settingsHelper";
+
+test.describe('timeslider line numbers', function () {
+  test.beforeEach(async ({context}) => {
+    await context.clearCookies();
+  });
+
+  test('shows line numbers aligned with the rendered document lines', async function ({page}) {
+    const padId = await goToNewPad(page);
+    await clearPadContent(page);
+    await writeToPad(page, 'One\nTwo\nThree');
+    await page.waitForTimeout(1000);
+
+    await page.goto(`http://localhost:9001/p/${padId}/timeslider`);
+    await page.waitForSelector('#timeslider-wrapper', {state: 'visible'});
+    await page.waitForSelector('#sidediv.sidedivdelayed', {state: 'attached'});
+    await page.waitForTimeout(1000);
+
+    await expect(page.locator('#sidediv')).toBeVisible();
+    await expect(page.locator('#sidediv .line-number').nth(0)).toHaveText('1');
+    await expect(page.locator('#sidediv .line-number').nth(1)).toHaveText('2');
+    await expect(page.locator('#sidediv .line-number').nth(2)).toHaveText('3');
+
+    const counts = await page.evaluate(() => ({
+      docLines: document.querySelector('#innerdocbody')?.children.length,
+      gutterLines: document.querySelector('#sidedivinner')?.children.length,
+    }));
+    expect(counts.gutterLines).toBe(counts.docLines);
+
+    const alignment = await page.evaluate(() => {
+      const innerdocbody = document.querySelector('#innerdocbody');
+      const sidediv = document.querySelector('#sidediv');
+      const docLines = [...document.querySelectorAll('#innerdocbody > div')];
+      const gutterLines = [...document.querySelectorAll('#sidedivinner > div')];
+      const sideRect = sidediv?.getBoundingClientRect();
+      const innerRect = innerdocbody?.getBoundingClientRect();
+      return {
+        gap: sideRect && innerRect ? Math.abs(innerRect.left - sideRect.right) : null,
+      };
+    });
+
+    expect(alignment.gap).not.toBeNull();
+    expect(alignment.gap!).toBeLessThanOrEqual(2);
+  });
+
+  test('inherits and persists the line-number preference from the shared cookie', async function ({page}) {
+    const padId = await goToNewPad(page);
+    await page.context().addCookies([{
+      name: 'prefsHttp',
+      value: encodeURIComponent(JSON.stringify({showLineNumbers: false})),
+      url: 'http://localhost:9001',
+    }]);
+
+    await page.goto(`http://localhost:9001/p/${padId}/timeslider`);
+    await page.waitForSelector('#timeslider-wrapper', {state: 'visible'});
+    await showSettings(page);
+
+    await expect(page.locator('#options-linenoscheck')).not.toBeChecked();
+    await expect(page.locator('body')).toHaveClass(/line-numbers-hidden/);
+
+    await page.locator('label[for="options-linenoscheck"]').click();
+    await expect(page.locator('#options-linenoscheck')).toBeChecked();
+    await expect(page.locator('body')).not.toHaveClass(/line-numbers-hidden/);
+
+    await page.reload();
+    await page.waitForSelector('#timeslider-wrapper', {state: 'visible'});
+    await expect(page.locator('#options-linenoscheck')).toBeChecked();
+    await expect(page.locator('body')).not.toHaveClass(/line-numbers-hidden/);
+  });
+});