Local Calculation · Real-Time · Private
All-in-One Clock Tool
Five time-management tools in one workspace — alarm, timer, stopwatch, world clocks, and a live date/time format reference. Every calculation runs in your browser.
all-in-one-clock v2.1
24 major cities
Live times updated every second. Handles daylight saving automatically.
Live date & time formats
Click any value to copy. All formats refresh every second.
Time's up!
Your alarm is ringing.
Pick a tab, set your parameters, go
Five independent tools sharing one clean workspace. No sign-ups, no ads, no data leaves your browser.
Open a tab
Alarm, Timer, Stopwatch, World, or Formats — each is self-contained and remembers its state.
Configure
Enter values, pick sounds, or adjust options. Everything updates live as you type.
Start & track
Hit start. Stopwatch records laps, timer counts down, alarm waits for its moment.
Return anytime
Settings persist in localStorage — your last tab, values, and sound are ready on revisit.
Precision, privacy, and predictability
What this tool does with your time data — and what it deliberately does not.
100% local after load
All timing, audio generation (Web Audio API), and time-zone calculations run in your browser. Once the page is loaded, no input is sent to a server, stored, or logged.
Accurate to centiseconds
Stopwatch uses requestAnimationFrame with a monotonic clock for smooth 10ms updates. Timer ticks with drift compensation against the wall clock.
Private localStorage only
Your last selected tab, alarm time, timer inputs, and sound choice are saved locally. Clearing browser data removes them — nothing syncs anywhere.
Five tools, one purpose
Click any card to jump to that tab.
Alarm Clock
Set hour/minute, pick from four sounds, add a custom message. Fires while the tab is open — background or minimized.
Countdown Timer
Hours, minutes, seconds. Choose stop, restart, or count-up when it hits zero. Add a title like "Pomodoro" or "Tea".
Stopwatch with Laps
Centisecond precision. Record unlimited lap times with delta from the previous lap. Perfect for workouts and speedruns.
World Clocks
24 major cities across every continent. DST-aware via the browser's IANA time zone database — updates every second.
Date/Time Formats
25+ reference formats — ISO 8601, US, European, Unix timestamp, and more. Click any value to copy. Updates live.
Privacy-First
All five tools run locally. No sign-ups, no tracking, no server-side logs. Close the page — your settings stay in this browser only.
What it does, and what it does not
Clear boundaries so you know when to use this tool and when to reach for another.
What it does
- Five time tools in a single tabbed workspace.
- Alarm with four sounds, custom message, repeat toggle.
- Timer with three on-zero behaviors and custom titles.
- Stopwatch with unlimited laps and centisecond precision.
- World clocks for 24 cities with automatic DST handling.
- 25+ live-updating date/time format references.
- Full dark mode with system preference detection.
What it does not
- Fire alarms when the browser tab is fully closed — use OS alarms for that.
- Run multiple timers in parallel within one tab (use separate tabs instead).
- Replace OS-level reminders, calendar events, or cron jobs.
- Sync settings across devices — data stays in one browser only.
Common issues and fixes
Quick answers to the most frequent problems.
Alarm didn't fire
The browser tab must remain open (can be minimized or in background). Closing the tab stops the alarm. Also ensure your system volume is up and the browser isn't muted.
Timer drifted over time
For very long timers, browsers may throttle background tabs. Keep the tab visible for best accuracy. Timer uses drift compensation on wake but cannot override browser throttling.
Stopwatch seems slightly off
Stopwatch uses performance.now() for accuracy, but the display updates every 10ms via requestAnimationFrame. For microsecond precision, use dedicated hardware.
World clocks show wrong time
Times come from your browser's built-in IANA time zone database. If a city's time looks wrong, your OS or browser may have outdated time zone rules — update your browser.
Frequently asked questions
Honest answers about the All-in-One Clock Tool.
Does the alarm work if I close the browser tab?
No. The browser tab must remain open for the alarm to fire, though it can be minimized or backgrounded. For guaranteed alarms that work when the browser is closed, use your operating system's built-in alarm app.
Can I run multiple timers at once?
This workspace runs one timer at a time within the timer tab. You can run an alarm, timer, and stopwatch simultaneously since they are independent tools. For multiple parallel timers, open the page in separate browser tabs.
Are my settings saved between visits?
Yes. Your preferences (alarm time, sound choice, timer inputs, last selected tab) are stored in your browser's localStorage only. Nothing is synced to a server — clearing browser data resets them.
How accurate is the stopwatch?
The stopwatch displays time to 1/100 of a second (centiseconds) using requestAnimationFrame for smooth updates. For microsecond-level precision required in scientific or professional sports timing, dedicated hardware is recommended.
Do world clocks update when daylight saving time changes?
Yes. The world clocks use the browser's Intl.DateTimeFormat API with IANA time zone names, which automatically accounts for daylight saving transitions based on your browser's time zone database.
Is my time data sent to a server?
No. All timing, alarm logic, and format calculations run locally in JavaScript after page load. No input is transmitted to AllInOneTools or any third party, and no server logs record your activity.