EST and PST8PDT resolve fine today and opt a resource out of DST forever

'EST', 'PST8PDT', and a raw UTC offset are all legacy or non-location zone forms that Intl happily resolves -- and each one silently opts a resource out of future daylight-saving changes.

This is one of the things Scheduling & Availability Core already handles. Bookings and availability that survive timezones, repeating events and daylight saving — without double-booking.

Buy for $993 of 3 clean-room builds passed · full refund if it fails on your machine

Is this you?

Accepting 'EST' or '+05:30' as a resource's timezone works today -- Intl resolves both without error -- and stores something that can never track a government's future DST rule change, because those forms carry no location. Only a real IANA Area/Location identifier can look up what the correct offset is at any future date; a bare offset or a legacy abbreviation is frozen the moment it's stored.

Why this one is easy to get wrong

The runtime doesn't distinguish 'this zone string resolved successfully' from 'this zone string will still be correct next year' -- Intl.DateTimeFormat happily accepts EST, PST8PDT, and a numeric offset without complaint, so nothing about writing basic validation (does this string resolve?) surfaces that some resolvable strings are still the wrong kind of value to store.

What you get instead

isValidZone() specifically rejects legacy tzdb entries with no location and any offset-shaped string -- '+05:30', 'UTC+5', 'GMT+2' -- along with a lowercase 'america/new_york', since IANA identifiers are case-sensitive. Only UTC and a proper Area/Location form pass, on the tz database's own stated theory: offsets are frequently guesswork and change on a government's schedule, but zone names are stable.

Source: ARCHITECTURE.md 'Zone identity (decided)' — checkable in the pack you receive

How you actually use this

You don’t install a library or wire up an SDK. Your own coding agent builds the code in your project, and you keep it — no runtime dependency on us.

Step 1
Download and unzip
You get a folder: the docs that tell an agent what to build, a starting skeleton, and the test suite that decides when it's done.
Step 2
Open it in Claude Code or Cursor
Point your coding agent at the folder. Nothing to install, no account with us, no API key.
Step 3
Paste one prompt
The pack contains the exact prompt. Paste it as your first message and leave it alone — it works through the build itself, choosing a cheaper or stronger model per task.
Step 4
Run ./verify.sh
One command. It prints a pass or fail for every check. Green means the build is done — the same script we ran to produce the receipt on this page.

Typical build: about 22 minutes of your agent working, mostly unattended. Then you integrate the working module into your app the way you would any code you’d written yourself.

Why you can believe this

3 of 3 runs passed

We ran this pack from an empty folder 3 times and published exactly what happened — every check, the model, the token cost, the wall time. Not a testimonial, and not our opinion: the same verify.sh you run yourself. Read the full receipt →

Buy for $99 14-day refund if verify.sh fails →