World Clock
Show the current civil time in several IANA zones, updated every second, starting from your zone plus three fixed ones.
Processed entirely in your browser — nothing you enter here is ever uploaded.
Result
About this tool
On load the page fills a zone menu from the IANA list the runtime exposes, grouped by country when the built-in country table has a code for that zone. It then builds a set of zones: the browser's resolved time zone, UTC, America/New_York, and Asia/Tokyo. If your own zone is already one of those three, the set simply has fewer cards, because a Set drops duplicates. A preset may add further IANA names, and a name that is not in the runtime list is ignored. The Add button inserts whatever the menu currently points at. There is no remove control in the script, so a zone you add stays until you reload the page.
Every card shows one zone at the current instant, new Date() at the moment of the paint. The title is the IANA name with underscores turned into spaces, so America/New_York reads America/New York. The large line is the hour, minute, and second in the page language, using that zone. The small line is the short weekday, the short month, the day number, and the offset label for that zone at that instant. The offset is whatever the runtime reports for the zone on this date, including daylight-saving time when the zone is observing it. The cards are not four independent clocks that can be set to different dates. They are four views of one instant.
A one-second setInterval calls the same paint again. While the tab stays open, the seconds advance. Browsers may throttle timers in a background tab, so the digits can pause and then catch up when the tab is visible again. Closing the tab stops the timer. Nothing is stored: the added zones live in a Set in the page, not in localStorage. The page does not convert a time you type. If you need 15:00 in London as a clock time in Tokyo on a chosen day, that is the time-zone converter, which parses a datetime. This page only answers what time it is now.
The city label is the last segment of the IANA name, not a translation of the city, except that underscores become spaces. Country groups in the menu use the page language's region names where Intl.DisplayNames can produce them. Zones without a country in the table are listed after the groups, with underscores replaced. The page does not show a map, does not search a city that has no IANA name, and does not schedule an alarm. New York and Tokyo are the fixed companions of UTC and your zone, not a list you can edit except by adding more.
Example. A browser in America/Chicago opens four cards: that zone, UTC, America/New York, and Asia/Tokyo. Each card is the current instant, and the seconds line is redrawn every 1000 ms.
Limit. The clocks show the present instant only. There is no remove button, added zones disappear on reload, and a background tab may delay the one-second timer.
Frequently asked questions
Which clocks appear when the page opens?
Your browser's IANA zone, UTC, America/New_York, and Asia/Tokyo. If your zone is already one of those, you see fewer cards because duplicates are dropped. A preset may add another zone from the same IANA list. An unknown name is ignored.
Can I look up a time on another day?
No. Every card formats new Date() in its zone. The page does not have a datetime field. A chosen civil time in one zone, shown in another zone, is the time-zone converter. This page is only the present instant, including the current daylight-saving offset.
How do I add a city, and how do I remove one?
Pick an IANA name in the menu and press Add. The script has no remove control. Reload the page to return to the original set. Added names are kept in memory for this visit only. They are not written to local storage.
Why did the seconds stop in a background tab?
The paint is window.setInterval at 1000 ms. Browsers often throttle timers in tabs that are not visible, then run them again when you come back. The time shown after that gap is the new current instant, not a count of missed ticks.