Unix Timestamp Converter — online, without uploading your files
A plain number is read as seconds or as milliseconds by its magnitude: below 100,000,000,000 it is treated as seconds, at or above that as milliseconds. That rule is worth knowing, because a genuine millisecond timestamp from before 3 March 1973 falls under the threshold and will be read as seconds. A number too large to be held exactly in JavaScript is refused with "The timestamp is outside the exact integer range." rather than being silently rounded. Anything that is not a plain integer is handed to the browser's own date parser, so an ISO 8601 string such as 2024-01-01T00:00:00Z works and anything the browser cannot read is refused with "The timestamp or date is not valid."
Quick Summary / Direct Answer
To convert a Unix timestamp without uploading anything: open the OpenTools timestamp converter, type a number or an ISO date into the box, and press Convert timestamp. It answers with three lines: the UTC time in ISO 8601 form, the Unix value in seconds, and the Unix value in milliseconds.
Tool Specifications
Runs on
Your browser
Server upload
None
Account
Not required
Cost
Free, no paywall
How to use Unix Timestamp Converter in 3 simple steps
Three steps, all of them inside this browser tab.
Open the Unix Timestamp Converter workbench
Open the workspace in your browser. The code it needs loads with the page — there is nothing to install and no account to create.
Provide your input files or parameters
Select, drag, or configure your input. The file is read into the page and processed there, so there is no upload to wait for.
Save your output
Preview the result and click download. The file is written from the page straight to your disk; nothing is stored on a server.
Local Browser Compute vs. Traditional Cloud Converters
What changes when the tool runs in your own tab instead of on someone else's server.
| Feature / Aspect | OpenTools (Local) | Standard Cloud Converters |
|---|---|---|
| Where your file goes | Stays in the page; it never touches a server | Uploaded to and processed on the provider’s servers |
| Waiting to upload | None — there is no upload step | Upload time, then a place in the server queue |
| Price | Free, with no paywall and no sign-up | Often a free tier with daily limits or a subscription |
| Retention | Nothing to retain; the file was never sent | Stored on the provider’s disks under their policy |
| Account & tracking | No account, no third-party trackers, no client-side analytics | Often an email sign-up and advertising trackers |
How this page is locked down
This page is served with a Content Security Policy that blocks every network connection the page could make (connect-src 'none'). Your browser will not send the file, its name or its contents to any server, including this one. The exact header is below.
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Frequently Asked Questions
Does it show my local time zone?
No. Every answer is in UTC: the ISO line always ends in Z, and the two Unix numbers are time-zone independent by definition. There is no local-time output, no named time zone picker and no relative phrasing such as "two hours ago". If you need local time, convert it yourself from the UTC value shown.
How does it decide between seconds and milliseconds?
By size alone. An integer whose absolute value is below 100,000,000,000 is multiplied by 1,000 and treated as seconds; anything at or above that is treated as already being in milliseconds. In practice ten-digit timestamps are read as seconds and thirteen-digit ones as milliseconds, which is what almost every system emits, but a millisecond value from before March 1973 is small enough to be misread as seconds.
Can it handle dates before 1970?
Yes. Negative integers are accepted and converted the same way, so -86400 gives 1969-12-31T00:00:00.000Z. The Unix seconds line is rounded down towards the more negative value, so for a time before the epoch that carries fractional milliseconds the seconds line can sit one second earlier than a simple truncation would give.
What date formats does it accept as text?
Whatever your browser's date parser accepts, which reliably means ISO 8601: 2024-01-01, 2024-01-01T00:00:00Z, and offsets such as +05:30. Other formats are left to the browser and can differ between them, so a string like 01/02/2024 may be read differently in one browser than another, or refused outright. Using an ISO string removes the ambiguity.
Is there a download button?
No. The three lines appear in the result panel with a copy button, and unlike the other developer tools here there is no file to save, because the answer is three short lines. Nothing about the conversion leaves the page either way.
Does Unix Timestamp Converter upload my files or data to any server?
No. The work happens in the page you have open. This page is served with a Content Security Policy of connect-src 'none' and webrtc 'block', so the browser will not let it open a connection to any server, including this one.
Is Unix Timestamp Converter free?
Yes. There is no paywall, no usage limit and no account. If the tool is useful to you, you can choose to support the project.
Can I use this for confidential legal or financial records?
Your file is not sent anywhere, so it is not exposed to this site or to a third party. What remains is your own device and browser — treat it the way your organisation's policy treats any local file.
Does the site collect anything when I visit?
The server records one coarse metadata event per page visit (see the security policy for exactly what). There are no third-party trackers and no client-side analytics, and nothing from the tool itself — your files, inputs or results — is included.
Ready to use Unix Timestamp Converter?
Open the workspace in your browser. No account, no paywall, and your file never leaves the page.