Full-screen countdown timer with customizable alerts for rehearsing presentation timing.
This tool turns a browser tab into a full-screen countdown for rehearsing a presentation. You set a duration, the display fills the screen with a large remaining-time readout, and alerts you configure fire when the remaining time crosses chosen thresholds, so you can keep speaking without glancing at a wrist. The usual misreading is the alert units: an alert set at 2:00 means two minutes left, not two minutes after you start, so on a twelve-minute talk it fires at the ten-minute mark. It is a rehearsal aid, not an audience-facing stage clock.
A concrete input and expected output from the current implementation.
Input
Duration 5:00, alert at 1:00 remaining
Expected output
The overlay starts at 05:00 and counts down. When 1 minute of the 5 remains, after 4 minutes of speaking, the alert fires as the display reads 01:00. At 5 minutes the display reaches 00:00 and the countdown ends.
Alerts are keyed to remaining time, so the one-minute-left alert fires when four minutes have elapsed (300 seconds minus 60 seconds). The 01:00 display and the alert arrive together; that instant is the warning the speaker is meant to act on.
Set a total duration and the overlay fills the screen with a large remaining-time readout that counts down toward zero, sized so you can read it from across the room. The countdown runs locally in the browser tab; no network request happens and nothing is uploaded. Keep the tab in the foreground, because browsers throttle background tabs, which can make the count drift.
Alerts are keyed to remaining time, not elapsed time. Each alert names a point on the countdown, and when the display falls to that point the alert fires, typically as a color shift in the readout. Thresholds fire in descending order as the count passes through them, so you can stack warnings such as 3:00, 1:00, and 0:30 near the end of a long talk.
Its stated purpose is rehearsal: a full-screen countdown for practicing timing before the real run. Nothing prevents you from leaving it running during a live talk, but the tool is not described as an audience-facing stage clock, and a large countdown visible to the room often distracts more than it helps. Most presenters rehearse with it and present without it.
No. The tool runs entirely in the browser: the countdown is computed locally in the page, nothing is uploaded, and no network connection is needed once the page has loaded, so it keeps counting even with the network off. There is no account, no sync, and no telemetry. The one condition: the tab itself must stay open and in the foreground.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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