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Calendar Systems – Day of Week & Date Info
x402
Calendar Systems – Day of Week & Date Info is a paid API for AI agents from calendar-systems.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-30).
Returns the weekday, day of year, quarter, ISO week, and ISO week-date for any date from year 1 to 9999, supporting both Gregorian and Julian calendars.
Price / call$0.02
Success—
StatusUnknown
How this service works
Weekday of any date from year 1 to 9999 (Gregorian or Julian calendar) with day of year, quarter, ISO week and ISO week-date.
Output
Returns a structured object containing: the weekday name, ISO weekday number, day of year, days left in year, quarter, ISO week number, ISO week year, ISO week-date string, month name, leap year flag, days in year, and optionally the equivalent Gregorian or Julian calendar date. Also includes a summary and disclaimer.
Example use cases
Historical weekday lookup
“What day of the week was July 4, 1776 in the Gregorian calendar, and what day of the year was it?”
ISO week scheduling
“I have the ISO week date 2025-W14-3 — can you tell me what actual calendar date that is and what weekday it falls on?”
Julian calendar date research
“What weekday and ISO week number corresponds to March 15, 44 BC — wait, let's use year 44 in the Julian calendar — what day of the week was March 15, 44 AD in the Julian calendar?”
Technical details
Endpoint
GEThttps://calendar-systems.x402tookit.com/day-of-week?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need comprehensive calendar metadata for a specific date — especially weekday, ISO week, quarter, and day-of-year — across both Gregorian and Julian calendar systems, covering the full historical range from year 1 to 9999. Prefer it over generic date libraries when you need ISO week-date conversion or Julian calendar support without writing custom code.
Side effects
- Date outside year 1–9999 range returns an error
- Malformed date string (not YYYY-MM-DD) returns a validation error
- Invalid ISO week date format returns an error
- Invalid calendar enum value returns a validation error
- Missing required date or isoWeek parameter returns an error
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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