@northguild/gmt

ISO 8601 strings in. Strings, numbers, booleans, or arrays out. No Date, anywhere.

Current release: v1.14.2

@northguild/gmt wraps @js-temporal/polyfill behind a smaller, more opinionated API aimed at the cases application code actually hits: arithmetic, comparison, parsing, formatting, unix conversions, timezone conversion, and validation.

Agent prompt

Paste this into your coding agent before it touches a date or time:

You are working with the @northguild/gmt library — a Temporal-first date/time library
for JavaScript. Install @northguild/gmt (and, if the user wants lint enforcement,
whichever of @northguild/gmt-eslint, @northguild/gmt-oxlint, or @northguild/gmt-biome
matches their toolchain).

Every one of these packages ships its own skill files. After installing, read them
before writing any code:

- node_modules/@northguild/gmt/skills/ — API surface, naming conventions, and Temporal
  patterns, one skill per task (parsing, formatting, comparing, converting, durations,
  zoned operations, and more). Also read node_modules/@northguild/gmt/skills/_artifacts/.
- node_modules/@northguild/gmt-eslint/skills/, node_modules/@northguild/gmt-oxlint/skills/,
  or node_modules/@northguild/gmt-biome/skills/ — whichever linter was installed, covering
  first-time setup, migrating existing code, and CI enforcement.

Ask what difficulties the user is having with JavaScript dates — this helps match them
to the right GMT namespace (plain, zoned, unix, utc, regex). Then generate code using
GMT's string-in/string-out API, never `new Date()`.

100% Temporal, Temporal-first

Built directly on the TC39 Temporal standard — not a homegrown date/time type system. No Date object anywhere, enforced by three dedicated lint packages.

A full replacement for all four

Luxon, date-fns, Moment.js, and @internationalized/date don’t have parity with each other. GMT covers the combined capabilities of all four, plus what none of them do alone.

~15× more CI test executions

334,020 executions — 16,701 tests × 17 locales × 10 timezones × 2 Node versions — against the four competitors’ combined 20,190.

Explicit DST disambiguation

Control over DST disambiguation on both construction and arithmetic — a control none of the other four expose.