About TimestampLens

TimestampLens is a set of browser-only tools for the ways computers write down moments in time: Unix timestamps, time zones and daylight saving, ISO 8601 and RFC 3339 text, durations, date arithmetic and the 32-bit limit of 2038.

Why it exists

Time looks simple and fails in confusing ways. The same moment is 1700000000 in one system and 1700000000000 in another. A day is not always 24 hours, and a clock time can be skipped or happen twice when the clocks change. 31 January plus one month is not a real date. PT36H and P1DT12H are different lengths on some days. A 32-bit counter stops at 03:14:07 UTC on 19 January 2038. TimestampLens does the conversion and then shows the working for your own input: what unit it guessed, which offset applied, whether the time exists, what each choice would produce. Each page lists real inputs that go wrong, with the exact output, and cites the document behind each rule.

What is on the site

• Unix epoch converter: seconds, milliseconds, microseconds and nanoseconds to a date, and back, with exact integers.
• Time zone converter that handles the clock times skipped or repeated by daylight saving.
• DST transition finder: every offset change of a zone in a year, to the second.
• ISO 8601 and RFC 3339 validator with the reason a string fails.
• ISO 8601 duration calculator, including applying a duration to a date.
• Date calculator: differences, and adding or subtracting, with daylight saving and month ends.
• Year 2038 problem: what a 32-bit timestamp does, with a live demonstration.

There are no separate pages for variations of the same task (for example one page for each time zone pair): they would run the same engine and show the same tables, so the tools take the zones as input instead.

Everything runs in your browser

The tools are TypeScript running on your device, using arbitrary-size integers (BigInt) so that large timestamps are exact. What you type or paste is not sent to a server. Pages are static files; there is no back end that receives your input. The time zone rules come from your own browser's copy of the IANA time zone database; nothing is downloaded. The details, including the one setting key the site stores in your browser's local storage, are in the Privacy Policy.

How the results were checked

• Hand-derived expectations. Expected values in the tests were worked out on paper first (days-from-civil arithmetic, ISO week rules, transition dates) and only then compared with the code, so a bug in the code cannot quietly become the expected answer.
• Independent implementations. The tests compare the engine with other software on thousands of inputs: the calendar and week arithmetic against Python's datetime, and the time zone transitions and local-time resolutions of 41 zones against Python's zoneinfo and Go's time package, using fixtures generated from the same 2026c time zone database; epoch conversions against JavaScript's Date and BigInt; the leap-second list against the IANA file.
• Code in other languages was run. The JavaScript, Python, Go and SQLite snippets on the pages were executed and the printed output is what each snippet printed. The Java, PostgreSQL and MySQL snippets were not run, and each says so.
• Every example on a page is a test. The inputs and outputs shown under "Worked examples" and "What goes wrong" are recomputed by the same engine in an automated test, so a page cannot show a value the tool would not print.
• Real browser test. The built site was loaded in headless Chrome under different time zone settings (including one with daylight saving) and each tool was run with a known input, because tests of the code alone cannot show a button that is not wired up.

Where it is unsure

Each page has a section on limits. The ISO 8601 standard itself is sold, not free, and was not read; the validators follow RFC 3339 and a published summary and say so. The Temporal verdict for durations comes from MDN's documentation, not from running Temporal. Local times depend on the time zone data your browser carries, which can lag behind rule changes. Behaviour that comes from observing software rather than from a specification is labelled as observed. Every page ends with the documents it relied on, with links and the date they were read. If a result disagrees with your own software, please tell us with the input, the options and what you saw; that is the most useful kind of correction.

Who runs it

TimestampLens, an independent project operated from Indonesia. You can reach us by email at joe@zona13.net.

Cost and advertising

The site is free. As of 3 October 2026 it shows no advertising, uses no analytics and sets no cookies. If any of that ever changes, the Privacy Policy and this page will be updated before it does.

What it is not

It is not an official time source, a legal or financial calculation tool, or a substitute for testing your own code. Libraries and databases differ from the idealised results shown on some pages (the pages show several of these differences). Treat the output as a well-checked second opinion and see the terms and disclaimer.