OpenWorkdays — business-day date math, no signup.

Add/subtract working days, count business days between two dates, or test if a date is a business day — with YOUR holiday list. No account, no API key, one GET. Built so AI agents get deterministic date math (LLMs are unreliable at it).

Live demo

// JSON response shows here

curl — copy & paste

curl "https://openworkdays.vercel.app/api/businessdays?start=2026-05-15&days=5"

curl — business days between two dates

curl "https://openworkdays.vercel.app/api/businessdays?start=2026-05-15&end=2026-06-15&holidays=2026-05-25"

JavaScript

const base = "https://openworkdays.vercel.app";
const r = await fetch(
  base + "/api/businessdays?start=2026-05-15&days=5"
);
const out = await r.json(); // { mode:"add", result:"2026-05-22", resultWeekday:"fri", ... }

Limitations