A zero-signup business-day date arithmetic API that allows adding/subtracting working days, counting business days between two dates, and testing if a date is a business day, with custom holidays.
Enables Japanese business calendar operations such as holiday checking, business day calculations, payment date calculation, fiscal year determination, and deadline tracking, all locally without external API.
Provides Japanese business day calculations: add or subtract business days, count between dates, check whether a date is a business day, and reverse-calculate deadlines. Handles national holidays and year-end periods fully offline with no API keys required.