Convert between Unix epoch timestamps and human dates. Auto-detects seconds vs milliseconds. Shows UTC and local timezone. Nothing leaves your browser.
Paste a Unix epoch value and get the corresponding UTC date-time plus your local time, as reported by your own browser. The tool auto-detects whether the number is in seconds (10 digits) or milliseconds (13 digits), so you do not have to divide by 1000 yourself. You can also go the other way: pick a date and time to get the epoch back.
The "local" time shown is whatever timezone your operating system is set to; Sunasty does not know or store your location.
No. Every operation runs inside your browser tab using JavaScript and WebAssembly. Your file is read into memory on your own device, processed there, and the result is offered as a local download. Nothing is transmitted to Sunasty or any third party. You can verify it yourself: open your browser DevTools, go to the Network tab, and watch, no request carries your file.
The browser's Intl.DateTimeFormat API is used to format the date in your OS timezone. Sunasty never reads or stores your location, the local offset is supplied by the browser itself and never transmitted anywhere.
Yes. A value with 10 or fewer digits is treated as seconds; 13 or more digits as milliseconds. You can also manually override the unit if your timestamp falls in an ambiguous range.
Yes, once the page has loaded. Because the processing happens on your device, you can disconnect from the network and the tool keeps working. This is the clearest proof that your data never leaves your machine.
It is completely free and requires no sign-up. There are no watermarks, no daily limits and no tracking cookies needed to use the tool.