TZ History Every time zone change, ever made, explained

API Documentation

Access exact historical time zone offsets, Daylight Saving Time status, and transition gaps/overlaps programmatically via our edge API.

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Endpoint: GET /api/v1/at

Evaluates the offset, abbreviation, daylight saving state, and rule in force for a specific region and timestamp.

Request Parameters

Parameter Type Required Description
zone String Yes Canonical IANA time zone identifier (e.g. America/New_York, Europe/London).
t String Yes Timestamp in ISO 8601 format (e.g. 2026-03-08T02:30:00) or epoch seconds.

Response Schema (Unambiguous Standard / DST)

{
  "zone": "America/New_York",
  "query_time": "2026-07-01T12:00:00",
  "status": "normal",
  "utc_iso": "2026-07-01T16:00:00Z",
  "offset_seconds": -14400,
  "offset_str": "-04:00",
  "abbr": "EDT",
  "is_dst": true,
  "rule_in_force": "US"
}

Response Schema (Spring Forward Gap)

When the requested wall-clock time was skipped during a spring-forward transition:

{
  "zone": "America/New_York",
  "query_time": "2026-03-08T02:30:00",
  "status": "gap",
  "message": "Local wall-clock time did not exist due to a spring-forward transition.",
  "transition": {
    "instant_utc": "2026-03-08T07:00:00Z",
    "wall_time_before": "2026-03-08 02:00:00",
    "wall_time_after": "2026-03-08 03:00:00"
  },
  "candidate_standard": {
    "offset_str": "-05:00",
    "abbr": "EST",
    "utc_iso": "2026-03-08T07:30:00Z"
  },
  "candidate_daylight": {
    "offset_str": "-04:00",
    "abbr": "EDT",
    "utc_iso": "2026-03-08T06:30:00Z"
  }
}