⏳ Countdown Timer

🎯 Target date & time

When should the timer hit zero?

Local wall-clock time. The browser converts this to an absolute instant before subtracting Date.now().

🔧 Controls

Play audio cue when the timer hits zero

⏱ Remaining

Target: {{ formattedTarget || '—' }}

Status: {{ finished ? 'finished' : (running ? 'running' : 'idle') }}

🔔 Time's up!

The countdown reached zero. Pick a new target and press Start to count down again.

⚠️

ℹ️ About Countdown Timer

What this tool does

The Countdown Timer counts down to a target date and time of your choosing. Pick a future moment, hit Start, and the page renders a live HH:MM:SS display (DD:HH:MM:SS once the remaining window is at least a day). The browser tab title mirrors the same remaining time, so the countdown stays visible even when this tab is in the background. When the timer reaches zero, the UI flips to Time's up and a short audio cue plays.

How it works (technical details)

Pure client-side. The target time you enter, the current time, and the remaining milliseconds are all computed in your browser. No network request is made, and no data leaves the page.
Computation. The remaining time is Date.parse(targetIso) - Date.now(), recomputed every animation frame via window.requestAnimationFrame. Browsers throttle that callback in background tabs, but the next visible frame still uses fresh wall-clock time, so the display catches up rather than drifting.
Tab title updates. While the timer is running, the tool overwrites document.title with the remaining time so a glance at the tab bar tells you how long is left. Pausing or resetting the timer restores the page's original title.
Audio cue. When the timer hits zero, an 880 Hz sine tone plays for half a second using the Web Audio API. The cue can be toggled off with the checkbox in the input column. Some browsers require a user interaction (such as clicking Start) before they will play sound — clicking Start counts.
No timezone drift. The <input type="datetime-local"> returns the target in your local wall-clock time. Both the target and Date.now() resolve to the same absolute instant before subtraction, so daylight-saving transitions and host timezone differences do not change the remaining count.

Use cases

Release / launch countdowns — keep a tab pinned with the time to your next deploy, product launch, or content drop visible in the tab bar.
Event countdowns — anniversaries, birthdays, conference start times, sports kickoffs, exam start times.
Maintenance windows — visible countdown to a planned outage or service restart.
Cooking, focus sessions, breaks — short fixed-time countdowns with an audible end cue.
Pair work / meeting timeboxes — display a shared countdown during a meeting or pair-programming session.

Privacy note

The countdown computation, the formatted display, the tab-title updates, and the audio cue all run inside this page. No target time, no remaining time, and no audio data is sent to a server. There is no API endpoint for this tool — the algorithm is too trivial to be worth exposing, and the interesting behavior is entirely in your browser.

References

MDN — window.requestAnimationFrame — the timing primitive driving the per-frame recompute loop.
MDN — Date.parse — how the entered datetime string is converted to a millisecond timestamp.
MDN — Web Audio API — the API used to synthesize the end-of-countdown beep.
MDN — <input type="datetime-local"> — the input control used to pick the target moment.
For HH:MM:SS arithmetic without a target wall-clock instant, see the Time Duration Calculator.
For a one-shot wall-clock breakdown (next birthday, days alive), see the Age Calculator.