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IANA Local Time Resolver

Resolves a local wall-clock time with pinned IANA tzdb 2026d. Returns every valid UTC candidate for a repeated fall-back time, or the exact gap and shift-forward suggestion for a nonexistent spring-forward time.

When to use

You must safely turn a named-zone local time into an instant, validate a scheduled time around a daylight-saving transition, or preserve every possible interpretation instead of silently choosing one.

Do not use when: The input already includes a numeric UTC offset or Z, the task only needs the current clock time, or latitude/longitude must first be mapped to a zone.

Example user requests

Resolve 2026-11-01 01:30 in America/New_York and return both UTC candidates.
Does 2026-03-08 02:30 exist in New York? Show the DST gap.
判断 Australia/Adelaide 的 2026-10-04 02:30 是否存在，并给出时区数据版本。

Formula

for each zone offset o: candidate_utc = local_wall_time + o; keep candidates whose active offset at candidate_utc equals o

Calcgrid enumerates the offsets in the pinned zone record, verifies each candidate against the transition table, and returns zero, one or multiple candidates without asking the Worker runtime's mutable Intl/ICU database.

Inputs

Parameter	Type	Unit	Required	Description
`local_datetime`	string		yes	Wall-clock date and time without Z or a numeric offset; it will be interpreted only in time_zone.
`time_zone`	string		yes	IANA zone identifier present in tzdb 2026d.

Outputs

Output	Type	Description
`local_datetime`	string	Normalized input wall-clock time.
`time_zone`	string	Zone identifier supplied by the caller.
`resolved_zone_id`	string	Zone record used by the pinned data build.
`status`	string	unique, ambiguous (two valid instants) or nonexistent (inside a clock-forward gap).
`candidate_count`	integer	Number of valid UTC instants for the wall-clock input.
`candidates`	list	Every valid instant with UTC time, local time, offset and abbreviation, ordered earliest first.
`gap`	object	Clock-forward gap and shift-forward suggestion; null/omitted when the time exists.
`related_transition`	object	Transition whose overlap or gap contains the input, when applicable.
`previous_transition`	object	Previous offset change in this zone.
`next_transition`	object	Next offset change in this zone.
`tzdb_version`	string	Pinned IANA release used for every offset and transition.
`dataset_version`	string	Immutable Calcgrid evidence-package version.
`source_url`	string	Version-specific official IANA release URL.
`source_sha256`	string	SHA-256 of the downloaded official IANA tzdata release artifact.
`coverage_note`	string	Coverage and rule-change limitations for this fixed version.

Example

New York fall-back overlap: {"local_datetime":"2026-11-01T01:30:00","time_zone":"America/New_York"} → {"status":"ambiguous","candidate_count":2,"candidates":[{"utc_datetime":"2026-11-01T05:30:00Z","utc_offset":"-04:00"},{"utc_datetime":"2026-11-01T06:30:00Z","utc_offset":"-05:00"}],"tzdb_version":"2026d"}

New York spring-forward gap: {"local_datetime":"2026-03-08T02:30:00","time_zone":"America/New_York"} → {"status":"nonexistent","candidate_count":0,"gap":{"duration_seconds":3600,"suggested_shift_forward_local":"2026-03-08T03:30:00"}}

GET https://tttkmbb.com/api/v1/calculate/local-time-resolver?local_datetime=2026-11-01T01%3A30%3A00&time_zone=America%2FNew_York

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/local-time-resolver (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/local-time-resolver · Markdown: https://tttkmbb.com/time/local-time-resolver.md · JSON definition: https://tttkmbb.com/time/local-time-resolver.json
MCP: server https://tttkmbb.com/mcp, tool resolve_local_time
OpenAPI operationId: resolve_local_time
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

IANA Time Zone Database 2026d (standard)
IANA tz database LICENSE (license)
Moment Timezone 0.6.4 data build (implementation)

FAQ

Why can one local time have two answers?

When clocks move backward, a range of wall-clock labels repeats under two offsets. The resolver returns both instants instead of guessing.

Is this based on the server's current time-zone database?

No. Results are fixed to IANA tzdb 2026d and include the release URL and SHA-256 so they can be reproduced.

Related calculators

Time Zone Converter — Convert one resolved wall time to a target zone.
IANA Time Zone Transition List — List every offset transition in a date range.
Unix Timestamp Converter — Convert a known instant to epoch seconds.