twineconvert

free · in-browser · no upload

Unix timestamp to ISO 8601
Converter

Drop your Unix timestamp file. We'll convert it to ISO 8601 right here in your browser, your file never leaves your device.

or drop your file

Select your file here to get started

or drop your file here.

Accepts .txt

nothing uploaded no file size cap no signup

How it works

Three steps. No upload, no signup.

  1. 1

    Drop your file

    Click the dropzone above or drag a Unix timestamp from your desktop. Files of any size, there's no upload, so there's no upload limit.

  2. 2

    Convert in your browser

    The conversion runs entirely in this tab using JavaScript and WebAssembly. Your file never touches our servers, we don't have any.

  3. 3

    Download

    Get your ISO 8601 the moment the conversion finishes. Convert another, or close the tab.

Files stay on your device

Your file is never uploaded. The entire conversion runs in your browser using WebAssembly. We can't see what you convert because we have no server to see it.

No file size limit

Server converters cap free users at 1-2 GB and gate larger files behind a paid plan. Since nothing uploads, our limit is whatever your browser can handle.

Free, no signup, no ads on conversions

No account required. No watermark on the output. No queue. Drop a file, get a converted file.

Why convert Unix timestamp → ISO 8601

What this conversion is actually for

Server logs, database timestamps, and analytics warehouses store time as Unix timestamps for compactness and timezone-neutrality. Humans read ISO 8601 (`2024-06-10T14:30:00Z`). Translating columns of timestamps is a daily task in log analysis, incident postmortems, and data exploration — and you don't want to paste timestamps into a remote tool that might log them.

A real example

You're reading an incident log. The time column is `1717977600`, `1717977901`, `1717978122` etc. Convert to ISO and now you can see at a glance that the events happened on June 10, 2024 around 00:00 UTC, ~5 minutes apart.

Troubleshooting

ISO output shows midnight UTC but I expected my local time.

Unix timestamps have no timezone (they're seconds since 1970-01-01 UTC). We always output UTC for portability. To shift to local time, parse the ISO string with `new Date(iso)` in JS — the Date object localizes automatically when displayed.

Negative timestamps fail.

Pre-1970 dates are negative Unix timestamps. We support them: -1000 = 1969-12-31T23:43:20Z. If yours fail, check the input has no thousands separators or trailing whitespace.

Formats involved

About Unix timestamp and ISO 8601

Unix timestamp, Unix epoch seconds

A Unix timestamp is the number of seconds (or milliseconds) since 1970-01-01T00:00:00 UTC, the moment the original Unix systems counted from. Compact, language-neutral, and never affected by timezone or DST changes. Logged by every server log line, returned by every API time field, stored in every analytics warehouse. Auto-detection is straightforward: 10-digit values are seconds, 13-digit are milliseconds.

How to open

Any tool that handles numbers. To make readable: every programming language has a function (`Date.now()` in JS, `time.time()` in Python, `date -d @<ts>` on Linux/Mac).

Full Unix timestamp format guide →
ISO 8601, ISO 8601 date/time string

ISO 8601 is the international standard for representing dates and times as strings: `2024-06-10T14:30:00Z` (UTC) or with explicit offset (`2024-06-10T14:30:00+02:00`). Unambiguous, sortable lexicographically, and the format every modern API uses (REST, GraphQL, JSON Schema). Standardized in 1988; the JavaScript `Date.toISOString()` and Python `datetime.isoformat()` both emit it.

How to open

Any text editor or programming language. To parse: every language ships a function (`new Date(iso)` in JS, `datetime.fromisoformat(iso)` in Python 3.11+).

Full ISO 8601 format guide →

FAQ

Common questions

Is this Unix timestamp → ISO 8601 converter really free?

Yes. No signup, no watermark, no daily file count limit. Every conversion runs in your browser, your file never touches our servers because there are no servers.

Where does my file go when I convert it?

Nowhere. The conversion runs entirely in your browser using JavaScript and WebAssembly. Your file is never uploaded to our servers. We don't have any servers handling files, there's nothing for us to log, store, or accidentally leak.

What's the maximum file size?

Whatever your browser can hold in memory. Practically, this means a few hundred MB on most computers, significantly larger than the 1-2 GB caps that server-upload converters charge for. Very large files (multi-GB) may require closing other browser tabs first.

Why convert Unix timestamp to ISO 8601?

Compact, timezone-neutral timestamp storage in logs and APIs. Timezone-explicit timestamp exchange in APIs and data files. The most common reason to convert is compatibility, ISO 8601 works in places where Unix timestamp doesn't, or vice versa.

How do I open a Unix timestamp file in the first place?

Any tool that handles numbers. To make readable: every programming language has a function (`Date.now()` in JS, `time.time()` in Python, `date -d @<ts>` on Linux/Mac).

Does this work offline?

Once the page is loaded, the conversion itself runs entirely offline. The first time you use a tool, your browser downloads the conversion library (a one-time cache). If you reload while offline, the page won't load, but you can install the site as a Progressive Web App for full offline use.

Can I convert multiple files at once?

Single file at a time for now. Batch conversion is on the roadmap, for now, drop one file, download the result, then convert the next.