How Zeitwide decides a business day

The Java API, the hosted MCP server and the open Python library all follow these rules, and a shared conformance suite checks that they give the same answers for the same dataset release.

One calendar, one date

• Coverage. A calendar that closes on holidays covers 1 January of its first year to 31 December of the last year in which it has a recorded entry. A date outside that is out_of_range: Zeitwide never guesses beyond what the sources published. FedNow closes on no holiday, so it has no limit.
• Entry. If the date has an entry (a published or projected closure, or an opening on an otherwise closed day), the entry decides.
• Weekend rule. With no entry, the date is open unless its weekday is one of the calendar's weekend days.

Several calendars

Calendars combine with all_open (the default: every calendar is open) or any_open (at least one is). If any of them is out of range, so is the answer.

Operations

• is_business_day(date): the rules above.
• next_business_day(date): the first business day after the date, never the date itself.
• add_business_days(date, n): moves n business days, backwards when n is negative. The start date doesn't count, and n = 0 returns it. Every day passed over that isn't a business day is listed in skipped, in the order met.

Where the data comes from

Zeitwide monitors each operator's official pages. A change is published only after two independent sources agree and a person reviews it. Each release is versioned (YYYY.MM.DD.N), and every answer names the release it came from, so it can be replayed as of any past moment.

• published dates are listed by the operator.
• projected dates are worked out by Zeitwide from the operator's published rules, before the operator lists them.