ガイド
タイムスタンプのタイムゾーン混乱をデバッグする方法
API・DB・フロント間で起きる時刻ずれを段階的に特定する手順です。
保存時刻と表示時刻の基準が混ざると、タイムゾーン問題が起きます。各変換点を追跡するのが近道です。
Find the source of truth
Identify where the original time is created and in what timezone.
Without this anchor, downstream debugging becomes guesswork.
Track conversions across layers
Check backend serialization, API transport, and frontend rendering separately.
A single implicit conversion can shift output by hours.
Use fixed test values
Test with known timestamps and compare expected vs actual at each step.
- Use UTC examples.
- Include DST boundary dates.
- Test from multiple client timezones.
Log timezone metadata
When possible, log timezone context alongside timestamp values.
This makes future incident debugging much faster.
Common scenarios
- API returns UTC but UI shows local time.
- Database values look shifted.
- Scheduled events fire at wrong hour.
- Reports differ by region.
Trace each conversion step
Write down source timezone, transport format, and display timezone for each layer to remove guesswork.