Quick reference
| Topic | Value | Use |
|---|---|---|
| UTC instant | 2026-07-16T00:00:00Z | Portable API timestamp |
| Offset time | 2026-07-16T08:00:00+08:00 | Local time with explicit offset |
| Date only | 2026-07-16 | Calendar date without time |
Practical notes
Use a trailing Z when the value is UTC. Use an explicit offset such as +08:00 when preserving local clock time matters. Avoid unlabeled local date-time strings in API payloads.
ISO 8601 strings sort correctly only when they use a consistent format and timezone. Normalize storage values to UTC when the goal is ordering, comparison, or deduplication.
| Check | Why it matters |
|---|---|
| Unit label | Field names such as created_at_ms or expires_at_s prevent seconds/milliseconds mixups. |
| Timezone | Store UTC or an explicit offset. Avoid server-local assumptions in jobs, logs, and API tests. |
| Round trip | Convert timestamp to ISO and back before shipping a parser or migration script. |