{"uid":"cap__8Sp7ONz50ylErTBOl3QS","slug":"calendar-systems-day-of-week-date-info-94f18116","name":"Calendar Systems – Day of Week & Date Info","description":"Weekday of any date from year 1 to 9999 (Gregorian or Julian calendar) with day of year, quarter, ISO week and ISO week-date.","url":"https://calendar-systems.x402tookit.com/day-of-week?utm_source=zero.xyz","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET"],"type":"string"},"queryParams":{"type":"object","required":[],"properties":{"date":{"type":"string","description":"YYYY-MM-DD, year 1 to 9999"},"isoWeek":{"type":"string","description":"ISO week date like 2026-W01-4 to convert to a calendar date instead"},"calendar":{"enum":["gregorian","julian"],"type":"string","description":"gregorian (default, proleptic) or julian"}}}},"additionalProperties":false},"output":{"type":"object","required":["type"],"properties":{"type":{"type":"string"},"example":{"type":"object","properties":{"asOf":{"type":["null","string"]},"date":{"type":["null","string"]},"source":{"type":["null","string"]},"isoWeek":{"type":["null","number"]},"quarter":{"type":["null","number"]},"reasons":{"type":["array","null"],"items":{"type":"string"}},"summary":{"type":["null","string"]},"verdict":{"type":["null","string"]},"weekday":{"type":["null","string"]},"calendar":{"type":["null","string"]},"degraded":{"type":["boolean","null"]},"leapYear":{"type":["boolean","null"]},"dayOfYear":{"type":["null","number"]},"monthName":{"type":["null","string"]},"daysInYear":{"type":["null","number"]},"disclaimer":{"type":["null","string"]},"notChecked":{"type":["array","null"],"items":{"type":"string"}},"isoWeekDate":{"type":["null","string"]},"isoWeekYear":{"type":["null","number"]},"gregorianDate":{"type":["null","string"]},"daysLeftInYear":{"type":["null","number"]},"isoWeekdayNumber":{"type":["null","number"]},"isoWeeksInThatYear":{"type":["null","number"]},"julianCalendarDate":{"type":["null","string"]}}}}}}},"responseSchema":null,"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.02","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.02/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.02","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_ABKVJ7qGDn08GkP-oHu8G","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.02","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"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.","exampleAgentPrompt":"What day of the week is July 4, 2026, and what ISO week number and quarter does it fall in? Use the Gregorian calendar.","exampleUseCases":[{"title":"Historical weekday lookup","prompt":"What day of the week was July 4, 1776 in the Gregorian calendar, and what day of the year was it?"},{"title":"ISO week scheduling","prompt":"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?"},{"title":"Julian calendar date research","prompt":"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?"}],"resultDescription":"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.","failureModes":["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"],"whenToPreferThis":"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.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-30T00:34:55.004Z","isFirstParty":false,"canonicalSlug":"calendar-systems-day-of-week-date-info-94f18116"}