The link is the sync

Why "just start a timer" doesn't work

If several people each start their own countdown for the same event, they'll start it a second or two apart — one clicked slightly later, one's app took a moment to load. Multiply that by a class or a webinar audience, and "everyone's timer" becomes many slightly different timers. The usual fix is a server acting as one central clock every device connects to. That works, but costs money per connected device, and is why most shared-timer products cap free viewers.

CountLink's approach

Instead of a server tracking how much time is left, CountLink calculates the one fact that matters (the exact moment the countdown should hit zero) the instant you press Start, and writes it into the URL as a timestamp. Anyone who opens that link, on any device, reads the same timestamp and subtracts it from their own clock. No round trip to a server is needed, because the link already contains the answer.

Step by step

1. Set a duration (directly on the board by rolling or typing the digits, or below it with a quick preset or an exact date and time) and, optionally, a label like "Exam ends."
2. The moment you press Start countdown, your browser calculates the target timestamp entirely on your own device.
3. That timestamp and label are encoded into a URL, which you send however you'd send any link.
4. Everyone who opens the link reads the same timestamp and starts a local countdown to it. Each device first checks its clock against a reference time and corrects it if it's out, so a projector whose clock has drifted still shows the room the right number.
5. Every screen reaches zero at the same instant, because they were always counting down to the same fixed point in time.

What this means in practice

No account. The countdown lives entirely in the link, so there's no user record to attach it to.

No viewer limit. Serving the same static page to one more viewer costs nothing, since nobody's holding a connection open per viewer.

Clocks are checked, not trusted. Each device does its own math, so on its own the countdown would only be as precise as that device's clock, and the machines rooms project from are the ones most likely to have drifted. So when a page loads it asks countlink.app for the time, the way network time sync does: it notes its own clock before and after the request, and if the difference is bigger than the round trip could explain, it counts down on corrected time and says so under the board. The request carries nothing about you or your timer. Screens agree to within about a second; a device that can't reach the site at that moment falls back to its own clock, exactly as before.

The trade-off, and the opt-out. On its own, a link carries one fixed instant and nothing can be pushed to it mid-countdown. With no ongoing connection between devices, there is no channel to broadcast a pause through, and the fix is starting a new countdown and sharing it. That is the default, and it is what keeps viewers free and unlimited. If you do need live control, tick phone control before you start: it opens that channel deliberately, for that one countdown, and gives you a second link that pauses, adjusts and stops it on every screen at once, still free and still with no cap on how many screens are watching. See everything CountLink does, or how it compares to real-time tools.