datetime-cz

name: datetime-cz description: Compute exact dates, weekdays, working days, Czech state holidays, DST transitions, and duration sums via the bundled `datetime.ts` Deno CLI. Use whenever the answer depends on a real calendar fact (today's date/weekday in Europe/Prague, holiday lookup, working-day count, Easter-derived dates, DST direction) or on summing hours/minutes (worklogs, time tallies). Triggers: "what day is X", "is X a working day", "working days in May", "when is Velikonoce / Velký pátek", "next Tuesday", "month-end date", "DST switch", any worklog/vacation calc or hour/minute sum. Do NOT guess or do mental math.

Deterministic date/time + Czech state holidays. Wraps Temporal API.

Default timezone Europe/Prague. Default locale cs-CZ. Holiday list = zákon č. 245/2000 Sb. (fixed days + Easter-derived: Velký pátek, Velikonoční pondělí).

When to use

Anything requiring today's wall-clock date/weekday → now.
"Is X a working day?", "how many working days in ?" → is-working-day / working-days. Never count by hand.
Czech state holidays in any year/range → holidays-year / holidays. Easter must be computed.
"Next Friday", "first Monday after X" → next-weekday.
Month/week/year start or end → period.
Date arithmetic (+ N days, - 3 weeks, etc.) → add.
Difference between two dates/datetimes → diff.
DST / 23h or 25h day questions → dst.
Summing a list of hour/minute durations (worklog totals, "does this add to Xh?") → sum. Never mental-math, even trivial sums.

If the answer depends on a fact this CLI returns, call it. Do not estimate, do not pattern-match from training data; Czech holiday law and DST rules are precise.

CLI

Run: $CLAUDE_SKILL_DIR/datetime.ts <command> [args...] (executable).

All output JSON on stdout. Errors → stderr, exit 1.

$CLAUDE_SKILL_DIR/datetime.ts now [tz]
$CLAUDE_SKILL_DIR/datetime.ts add <iso-date|datetime> '<json-duration>'
$CLAUDE_SKILL_DIR/datetime.ts diff <from> <to> [largest-unit]
$CLAUDE_SKILL_DIR/datetime.ts period <iso> <day|week|month|year> <start|end>
$CLAUDE_SKILL_DIR/datetime.ts next-weekday <1-7|cs-name> [from-iso] [inclusive]
$CLAUDE_SKILL_DIR/datetime.ts dst <year> [tz]
$CLAUDE_SKILL_DIR/datetime.ts is-working-day <yyyy-mm-dd>
$CLAUDE_SKILL_DIR/datetime.ts working-days <from> <to> [--list]
$CLAUDE_SKILL_DIR/datetime.ts holidays <from> <to>
$CLAUDE_SKILL_DIR/datetime.ts holidays-year <year>
$CLAUDE_SKILL_DIR/datetime.ts sum <duration> [<duration> ...]

largest-unit is one of years|months|weeks|days|hours|minutes|seconds (default days). ISO weekday: 1=po, 7=ne. Czech names accepted: pondělí úterý středa čtvrtek pátek sobota neděle. Duration JSON: any subset of {years, months, weeks, days, hours, minutes, seconds}, may be negative. sum duration tokens: bare number = hours (e.g. 1, 0.5), or unit-suffixed (1h, 30m, 45s, 1h30m, 2h15m30s). Negatives allowed. working-days --list appends dates: string[] (ISO YYYY-MM-DD, ascending) of every working day in range. Omit for count-only output. Use when you need the actual workday dates, not just totals — never hand-roll a day loop (DST off-by-one risk).

Examples

# Today in Prague
$CLAUDE_SKILL_DIR/datetime.ts now

# Working days in May 2026
$CLAUDE_SKILL_DIR/datetime.ts working-days 2026-05-01 2026-05-31

# Is Good Friday a working day?
$CLAUDE_SKILL_DIR/datetime.ts is-working-day 2026-04-03

# All CZ holidays in 2026
$CLAUDE_SKILL_DIR/datetime.ts holidays-year 2026

# Next Friday after today
$CLAUDE_SKILL_DIR/datetime.ts next-weekday pátek

# 90 days from a date
$CLAUDE_SKILL_DIR/datetime.ts add 2026-05-04 '{"days":90}'

# Hours/minutes between two timestamps
$CLAUDE_SKILL_DIR/datetime.ts diff 2026-05-04T09:00:00 2026-05-04T17:30:00 hours

# Last day of current month
$CLAUDE_SKILL_DIR/datetime.ts period 2026-05-04 month end

# DST transitions in 2026
$CLAUDE_SKILL_DIR/datetime.ts dst 2026

# Sum a list of worklog hours
$CLAUDE_SKILL_DIR/datetime.ts sum 1 1 1 5 1
# → total_hours: 9, formatted: "9h 0m"

# Sum mixed unit-suffixed durations
$CLAUDE_SKILL_DIR/datetime.ts sum 1h30m 45m 2h 15m
# → total_hours: 4.5, formatted: "4h 30m"

Notes

Script uses npm:temporal-polyfill. First run downloads to Deno cache (auto, no flags needed for module loading). Runtime perms: --allow-env only.
For "letošní/tento měsíc/zbytek měsíce" type questions: call now first, then derive bounds with period, then call working-days.
For "kdy bude volno": call holidays from today forward and next-weekday sobota — return whichever is sooner.
Velký pátek IS a state holiday (since 2016). Always treat as non-working day.