Unix Timestamp Converter Guide: Seconds, Milliseconds, UTC, and Local Time
Learn how Unix timestamps work, why seconds and milliseconds get confused, and how to convert API, log, and JWT dates safely.
- #developers
- #timestamps
- #debugging
- #tools
Unix timestamps are machine-friendly time
A Unix timestamp is a number that represents an instant in time. It counts from 1970-01-01T00:00:00Z, which is often called the Unix epoch.
Developers see timestamps in API responses, database rows, logs, webhook payloads, analytics exports, and authentication tokens because numbers are easy to store, sort, compare, and transmit.
Seconds and milliseconds are the common trap
Traditional Unix timestamps are measured in seconds. JavaScript Date values, many browser APIs, and some frontend logs use milliseconds instead.
That difference creates confusing bugs. If you treat milliseconds as seconds, the date may appear thousands of years in the future. If you treat seconds as milliseconds, the date may land near January 1970.
- 1717200000 is likely epoch seconds
- 1717200000000 is likely epoch milliseconds
- JWT exp, iat, and nbf claims are usually seconds
- JavaScript Date.now() returns milliseconds
UTC is the reference point
UTC is the shared reference timezone used by most servers, logs, and APIs. Local time is the same instant adjusted for the timezone configured in your browser or operating system.
When debugging systems across regions, start with UTC. It prevents daylight saving time and local offset confusion from hiding the real sequence of events.
Where timestamp conversion helps
Timestamp conversion is useful when a support ticket includes log values, an API response includes created_at fields, a database export uses epoch milliseconds, or a JWT contains exp and iat claims.
It also helps when writing documentation or tests. A readable ISO timestamp is easier for humans, while epoch values are often easier for systems.
Privacy matters for logs and tokens
A timestamp alone is usually low risk, but real snippets often include nearby user IDs, request IDs, emails, tokens, URLs, or tenant names. Uploading whole logs to random tools can expose more than the one number you meant to convert.
Use the smallest snippet possible. Convert the timestamp locally, then redact or remove surrounding sensitive data before sharing a support note or public issue.
Where tempboxs fits
The tempboxs Unix Timestamp Converter turns epoch seconds, epoch milliseconds, and date strings into UTC and local-readable outputs in your browser.
Use it alongside the JWT decoder, JSON formatter, and Base64 converter when debugging developer snippets without uploading pasted values to tempboxs.
Related tempboxs tools
Put the guide into practice with browser-only utilities that keep pasted values on your device.