What Is a Timestamp?
A practical explanation of epoch time, 10-digit vs 13-digit values, timezone effects, and conversion pitfalls.
Original source title: 时间戳是什么
Section 1
A timestamp is a numeric representation of time measured from a fixed starting point. In computing, the most common reference point is the Unix epoch: January 1, 1970 at 00:00:00 UTC. In simple terms, a timestamp says how many seconds or milliseconds have passed since that moment. This format is useful because computers can compare, sort, store, and transmit numbers more easily than formatted date strings. That is why timestamps appear so often in logs, databases, APIs, caches, queues, and order records.
Section 2
Many people first notice timestamps when they see a long 10-digit or 13-digit number in an API response or a database field. A 10-digit value usually means seconds, while a 13-digit value usually means milliseconds. These numbers look cryptic, but they correspond to a real point in time. Computers use them because time math becomes easy: compare two values, subtract them, and you can calculate intervals directly. Doing the same thing with many different date string formats is much more complicated.
Section 3
Timestamps often become confusing because of timezones and units. A common question is why the same timestamp turns into different clock times in different places. The answer is usually timezone conversion. The timestamp itself refers to a fixed moment, but when you display it, software may convert it into local time. Another common problem is mixing up seconds and milliseconds. If a millisecond timestamp is read as seconds, the result will be wildly wrong. Some systems also store timestamps as strings, which can look like ordinary text even though the value still represents time.
Section 4
For most users, the key idea is that timestamps do not exist to make time harder to read. They exist to make time easier for systems to process. That is why online tools so often provide timestamp-to-date conversion, date-to-timestamp conversion, second/millisecond conversion, and current timestamp lookup. These tools help users move between machine-friendly time values and human-friendly date formats. Once you connect timestamps to tasks like API debugging, log analysis, configuration, exports, and expiry calculations, they become much less abstract and much more practical.