Show a ChatGPT countdown timer full screen on a TV or projector

ChatGPT or Claude wrote you a countdown page for the start of a service, a class activity, or a break between talks. On your laptop it works. Now it has to fill the TV or the projector screen, stay on until zero, and not show a browser bar, a mouse pointer, or a sleeping screen halfway through.

Google's, Microsoft's, and Apple's help pages quoted here were read on November 4, 2026.

Open the file on the laptop that drives the screen

1. Connect the laptop and choose what the screen shows

Plug the laptop into the TV or projector. To show only the timer on the big screen while you keep your own screen, extend the display and drag the browser window onto the big screen. Mirroring shows the same on both.

2. Open the countdown file in a browser

Double-click the .html file. It should open in Chrome, Edge, Safari, or Firefox. If it opens as code in a text editor, see how to open it on Windows, a Mac, or a Chromebook. If all you have is code in a chat, Convika's free HTML viewer runs it in your browser to check it works, with nothing uploaded; to present it, save it as a file or publish it.

3. Go full screen

Click on the timer's page, then press the browser's full-screen key. The page's own full-screen button works too, if the AI gave it one.

4. Keep the screen awake and start the timer

Set the laptop so its screen doesn't turn off (next section), plug in its charger, and start the countdown.

Full screen on Windows, Mac, and Chromebook

The Windows and Mac keys are from Google's Chrome keyboard shortcuts, and the Chromebook key from Google's guide to the Chromebook keyboard.

Keep the screen from sleeping

A countdown that runs for 20 minutes outlasts many laptops' screen timeout. Change it before the event:

• Windows 11: Settings → System → Power & battery → Screen, sleep & hibernate timeouts. Set Turn my screen off after to a time longer than the event, for plugged in.
• Mac: System Settings → Lock Screen. Apple's settings are Turn display off on power adapter when inactive and Turn display off on battery when inactive. Set the one you'll use to a time longer than the event.

Some AI-made timers ask the browser to keep the screen on with the Screen Wake Lock API. MDN calls it a way "to prevent devices from dimming or locking the screen", but the system can refuse it, for example in power save mode or "if the document is not active or visible", and some browsers allow it only on an https:// page. Change the setting anyway.

Open it on a TV or another device

A file on your laptop opens only on your laptop. To open the countdown on a smart TV's browser, a tablet by the stage, or the venue's computer, publish it and open its link there:

1. Upload it. Drop the .html file into the box at the top of this page and click Get my preview link. That link works for 3 minutes, with scripts off, so the timer won't run in it. Click Keep this page — free, no card and sign up, and the page's scripts run.
2. Publish it. On the page's screen, click Publish page. Under Who can open this page?, choose Public and click Next. The first time, click Publish free. Under it, Publish without the Convika bar opens an order for Pro monthly ($12 a month, after a free 1-day trial with a card).
3. Open the link on the screen. Type the address from Live URL into the TV's or the computer's browser, or click Show QR code and scan it with a tablet. How to turn an HTML file into a QR code has the print and scan checks.

On Free, a small Convika bar sits at the foot of the page, and the browser's full-screen key keeps it on screen. Each time the page opens counts as a page view, out of 10,000 a month on Free. To fix the timer later, publish a new version at the same link: how to update an AI-made page at the same address. The same link and full-screen steps work for slides: see how to share HTML slides.

Ask ChatGPT for a better timer

A first countdown from an AI often uses small text, stops at zero without warning, and counts with a timer that can drift. Ask for these:

Make a full-screen countdown timer as one HTML file, with the CSS and
JavaScript inside it and nothing loaded from other addresses.

- Start time: [10:00]. Show minutes and seconds in digits as large as
  the screen allows, centred, light on a dark background.
- Work out the time left from the clock (the end time minus Date.now()),
  not by counting ticks, so it stays right if the browser slows the page.
- Change the colour at [2:00] left and again at 0:00. At zero, show
  [We're starting].
- Keys: Space starts and pauses, R resets, F toggles full screen.
- Hide the mouse pointer after 3 seconds without movement.
- Ask the browser to keep the screen on while it runs (Screen Wake Lock),
  and do nothing if the browser refuses.

Why the clock line matters: Chrome slows the timers of a page that's hidden. Google's Chrome team wrote that for a page hidden for more than 5 minutes, under certain conditions, "the browser will check timers in this group once per minute". A countdown worked out from the clock shows the right time again as soon as its page is visible. One that counts ticks can fall behind.

Open the result and let it run a full minute before the event. Then try every key.

For speakers: a timer that shows overtime

A countdown that stops at 0:00 tells a speaker they're out of time, and then nothing. For a talk, the speaker needs to see how far over they are. Fluxenic's free Stage Timer, on Blink Brief, fills the screen facing the speaker: it turns amber at 2 minutes left and red at 0:00, then counts the overtime as +0:01, +0:02, and shows a message you type under the time. Fluxenic is the company that runs Convika.

Frequently asked questions

Can ChatGPT make a countdown timer?

Yes. ChatGPT, Claude, or Gemini can write a countdown as one HTML file with its CSS and JavaScript inside. Ask for large digits, the time worked out from the clock, colours near the end, and keys to start and reset. Open the file in a browser to run it, or publish it to open it on another screen.

How do I make a countdown timer full screen?

Open it in a browser and press the full-screen key: F11 in Chrome on Windows, Fn+F in Chrome on a Mac, or the full-screen key on a Chromebook's top row. Press it again, or press and hold Esc, to leave. A timer the AI gave an F key or a full-screen button can do it from the page too.

How do I show a countdown timer on my TV?

Connect a laptop to the TV, open the countdown file in its browser, and go full screen. To use the TV's own browser instead, publish the file and type its link on the TV. Set the laptop's screen not to turn off for longer than the countdown.

Why does my countdown timer stop or fall behind?

Usually the screen went to sleep, or the page counts ticks and the browser slowed them. Set the screen timeout longer than the countdown, and ask the AI to work out the time left from the clock (the end time minus Date.now()) instead of counting ticks.

Sources

• Chrome Help: Chrome keyboard shortcuts (read November 4, 2026)
• Chromebook Help: Use your Chromebook keyboard (read November 4, 2026)
• Microsoft Support: Power settings in Windows 11 (read November 4, 2026)
• Apple Support: Change Lock Screen settings on Mac (read November 4, 2026)
• MDN: Screen Wake Lock API (read November 4, 2026)
• Chrome for Developers: Heavy throttling of chained JS timers beginning in Chrome 88 (read November 4, 2026)