Show HN: Meeting Timer for Google Slides, a countdown overlay for agenda topics

A free, open-source Chrome extension for Google Slides meetings with multiple speakers or topics and a fixed end time. Keep the time visible so everyone knows when to wrap up and move to the next presentation, conversation, or agenda item.

Mark the first slide of each speaker or topic, then set the meeting's start time and duration. The timer follows those sections and recalculates a share of the time left at each transition.

Add to Chrome — free · Try the interactive demo · Setup guide · Weekly-update template

Use it for workshops, panels, board or committee meetings, lessons, training, team updates, or any other meeting that uses Google Slides to move through a timed agenda. One person can lead several topics, several people can speak, or the meeting can mix both. No separate account or subscription. Settings stay in local browser storage.

A calm countdown in whole minutes. No seconds tick, so it never feels like an alarm.

Every section in slide order. Finished sections are checked, the current one is highlighted with an arrow, and upcoming ones wait. The card also says how many are left.

A gentle limit. When a turn runs out, the card turns amber and says "Wrap up". More than a minute over, it counts those minutes with a minus sign, in red, and the number fades slowly in and out.

Stays out of the way. After 5 seconds without a slide change, the card shrinks to a slim strip with the minutes, the sections left, and one dot per section. The next slide change brings the full card back.

Readable on any slide. The card is see-through, but it blurs and darkens what's behind it, so the text stays readable on white, black, or busy slides.

Follows your slides. You never touch the timer during the meeting: a turn starts when you reach the slide where the next speaker or topic begins.

Presenter-friendly. The overlay never takes focus or clicks, so you keep clicking or using the arrow keys to change slides. It works in fullscreen.

Each section gets an equal share of the time that's actually left when it begins:

time for this section = (start time + duration - now) / sections left

With 22 minutes left and 5 sections, the first person gets 22 / 5 = 4.4 minutes (shown as "4 min"). If they finish after 2 minutes, the next person gets 20 / 4 = 5 minutes. Short updates give time back to everyone after them, and long ones take it from the people still waiting.

This shares the remaining budget rather than guaranteeing equal total airtime. An early overrun can leave later speakers or topics with less time. The visible countdown supports shared time awareness; the facilitator still decides when to move on.

A section reached before the meeting's start time holds its full share until the meeting starts. Times always come from the wall clock, so a throttled background tab never drifts.

From the Chrome Web Store: Install Meeting Timer for Google Slides.

On another computer, run npm run build, copy dist/meeting-timer-overlay-<version>.zip, unzip it, and load the unzipped folder the same way.

One example: Download the editable weekly-update template. Upload it to Drive, open with Google Slides, and save it as a Google Slides presentation. See template instructions. Copying a deck does not transfer the extension settings; each organizer configures their own browser.

The setup (ticks, names, start time, and duration) is saved per presentation, so next week you only rescan and adjust. Rescanning keeps your ticks and edited names, matched by slide ID.

These work while the slides have focus, including in fullscreen. Change them at chrome://extensions/shortcuts.

The popup offers the same controls, plus Stop.

The extension has no servers, accounts, analytics, or remote code. Slide titles and settings stay in chrome.storage.local on your device. See PRIVACY.md for the full policy.

The content script matches all of docs.google.com/* rather than just /presentation/* because Slides runs its slideshow in about:blank frames and windows. Following those requires match_origin_as_fallback, which Chrome only allows with a /* path. On pages that aren't a Slides presentation, the script exits immediately.

File Role

extension/src/schedule.js Session model, the fair time split, and what the overlay shows

extension/src/slide_dom.js All Google Slides page knowledge: deck scanning and slide detection

extension/src/overlay.js The Shadow DOM card, its transitions, compact mode, and fullscreen handling

extension/src/content.js Ties storage, slide tracking, and the overlay together in Slides frames

extension/src/service_worker.js Keyboard shortcuts and the toolbar badge

extension/popup/ Setup and session controls

The active session lives in chrome.storage.local. Every Slides frame reads it, and whichever frame shows the presentation advances it.

Scanning fetches two views of the open presentation from docs.google.com with your existing session: /htmlpresent (Google's accessible HTML view) for slide titles, and /present (the slideshow page), whose embedded slide list flags each slide as shown or skipped. A slide's title is its most prominent text: the largest font, then the highest on the slide. The popup parses the HTML, because Slides pages enforce Trusted Types.

Slide detection in the slideshow uses, in order: the slide ID in the viewer's address, the navbar's slide position, and the slide's accessibility label.

The overlay lives in a closed Shadow DOM with pointer-events: none, so the page's styles can't break it and clicks pass through to the slides. In fullscreen it moves into the fullscreen element, because anything outside it is hidden.

Google Slides has no API for this without OAuth, so the extension relies on Slides' page structure:

Requirements: Node.js 20 or later. Rendering store images also needs Chrome or Chromium. The project has no npm dependencies: every script uses Node's standard library, so there's nothing to install.

npm test # unit tests (Node's built-in test runner) npm run build # validate the manifest and write dist/meeting-timer-overlay-<version>.zip npm run check # both of the above npm run icons # redraw extension/icons/.png npm run store-assets # re-render store/assets/.png with headless Chrome

After editing the extension, click the reload icon on its card in chrome://extensions and refresh open Slides tabs.

extension/ Exactly what ships: manifest, scripts, popup, icons tests/ Unit tests for the time split, Slides parsing, and the build helpers scripts/ build.mjs Manifest checks against store limits, then a reproducible zip make-icons.mjs Draws the icon at 16, 32, 48, and 128 px (no image tools needed) store-assets.mjs Renders screenshots and promo tiles through Chrome's DevTools protocol lib/ CRC-32, PNG, zip, and manifest helpers store/ listing.md Every Chrome Web Store field, ready to paste assets/ Screenshots and promo tiles templates/ The page those images are rendered from, using the real overlay and popup docs/ Static project website, setup guide, and editable meeting template marketing/ Launch drafts and free growth experiment tracker PRIVACY.md Privacy policy (link it in the store listing) CHANGELOG.md Release notes

Tests

npm test covers the time split (including the 22 / 5, then 20 / 4 example), turn handling (going back, jumping ahead, finishing), the compact view, slide-title extraction, hidden-slide detection against a captured Slides page, slide detection fallbacks, the manifest checks, and the zip writer. Overlay visuals are checked by eye: load the extension and present a deck, or run npm run store-assets and look at store/assets/.

store/templates/stage.html builds each scene with the extension's real schedule.js, overlay.js, and popup (with Chrome's extension APIs stubbed), so the screenshots always match the current design. npm run store-assets serves the repository on localhost, opens each scene in headless Chrome, and checks every image has the exact size the store requires. If Chrome isn't found, set CHROME_PATH:

CHROME_PATH="/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" npm run store-assets

Publishing to the Chrome Web Store

One-time setup

Sign in to the Chrome Web Store Developer Dashboard with the Google account that will own the listing. A dedicated account (or a group publisher) makes it easier to hand over later.

Pay the one-time US$5 registration fee and accept the developer agreement.

Turn on 2-Step Verification for the account. The store requires it to publish.

In Account, set and verify a contact email, and complete the trader / non-trader declaration (required for listings shown in the EU). A free personal project is usually non-trader.

Publish this repository (for example on GitHub) so the privacy policy, homepage, and support links in the listing are public.

Preparing a release

Update version in extension/manifest.json. Every upload must have a higher version than the last one.

Add the release to CHANGELOG.md.

Run npm run check.

If the overlay or popup changed, run npm run store-assets and review store/assets/.

Load extension/ unpacked and run through a meeting on a real deck: scan, start, present, advance, wait for compact mode, and stop.

First submission

In the dashboard, click New item and upload dist/meeting-timer-overlay-<version>.zip.

Fill in the Store listing, Privacy, Distribution, and Test instructions tabs from store/listing.md. It has every text field and maps each image to its file.

Click Submit for review. Reviews usually take a few days; you'll get an email. Chrome suggests leaving "Publish automatically after review" on unless you want to time the launch.

Updates

Prepare the release as above.

In the dashboard, open the item, go to Package, click Upload new package, and upload the new zip.

Update the listing text or images if they changed, then Submit for review.

Users get the update automatically within a few hours of approval.

Permissions without justification. The text for each one is in store/listing.md.

Undisclosed data handling. Keep the Privacy tab and PRIVACY.md in sync with what the code does if you add features.

Misleading branding. Keep "for Google Slides" wording and the non-affiliation note; don't use Google's logos in the icon or images.

Remote code. Never load scripts from the network; Manifest V3 forbids it.

Troubleshooting

Problem Fix

The popup says to open a Slides presentation Open the deck in the editor (/edit) in the active tab, then reopen the popup.

"Scan failed" Reload the Slides tab and retry. If it keeps failing, add sections manually.

The overlay doesn't appear in the slideshow Check the toolbar badge says ON, then press Alt+Shift+O in case the overlay is hidden.

The turn doesn't advance Check the right slides are ticked; press Alt+Shift+N to advance manually.

Nothing works after updating the extension Refresh the Slides tab so it picks up the new content script.

License

MIT. Meeting Timer for Google Slides is an independent project and isn't affiliated with or endorsed by Google. Google Slides is a trademark of Google LLC.

The static site is in docs/. See publication instructions for GitHub Pages setup, the intended canonical URL, and the post-publication checks. Website changes do not require a new extension release.