Korean Business Days API

There is no single “add N business days” endpoint here on purpose — business-day rules differ per app (some count Saturday, some observe company days). Instead, this API exposes the two primitives you actually need: the full holiday list for a year, and a one-call is-it-a-holiday check for any date. You loop your own date arithmetic on top, skipping weekends and any date the API flags as a holiday. Because substitute holidays (대체공휴일) are already in the dataset, your business-day math stays correct across the awkward cases that generic worldwide holiday lists miss.

Endpoints

Example request & response

curl "https://korea-calendar-api.kunstudio.workers.dev/v1/holidays/is?date=2026-09-25"

{
  "date": "2026-09-25",
  "is_holiday": true,
  "holiday": {
    "date": "2026-09-25",
    "name": "추석",
    "name_en": "Chuseok (Korean Thanksgiving)",
    "substitute": false
  },
  "weekday": "Fri"
}

No API key is needed on the origin to try this — it is rate-limited for fair evaluation. See the OpenAPI spec for the full schema.

Good to know

• Pattern: to add N business days, step one calendar day at a time; skip Saturdays/Sundays and any date where /v1/holidays/is returns is_holiday: true; stop when you have counted N working days. For a whole year, fetch /v1/holidays?year=YYYY once and build a local Set of holiday dates so you do not call the API in a loop.
• Substitute holidays (대체공휴일) are included in the dataset and flagged with substitute: true — this is the case most generic holiday lists get wrong and the one that breaks shipping/SLA math.
• Weekends are not holidays in the dataset (Korea's statutory holidays are date-based). Your business-day logic decides whether Saturday counts; the API only tells you the public-holiday and weekday facts.
• Bundled, verified years: 2026–2027. For production beyond that, the dataset syncs yearly from KASI 특일정보 (data.go.kr, KOGL Type 1, commercial use OK with attribution).

Related

Building a Korean fortune (사주/saju) app? Pair this with the KunStudio Saju API for a full four-pillars reading over REST.