Icyn Date

icyndate

Date context for AI agents and developers: lunar calendar, solar terms, holidays and "what does this day mean" — offline, verified, MIT. 给 AI Agent 和开发者的日期语义层：农历、节气、节假日、"这一天意味着什么"——离线、可验证、MIT。

Status: week 1. Lunar calendar, the 24 solar terms and the holiday layer (12 regions) are in; lunar & solar terms verified for 1900–2100, CN holidays for 2024–2026. 状态：第一周。农历、二十四节气、节假日层（12 个地区）均已落地；农历与节气 1900–2100 全量验证， 中国大陆节假日 2024–2026 逐天对拍。

Install / 安装

npm i @icyn/date                       # library: lunar + solar terms + CN holidays (~90 KB)
import "@icyn/date/regions/all";       # opt in to the other 11 regions (+ subdivisions), or "@icyn/date/regions/JP"

npx -y @icyn/date-mcp                  # MCP server for Claude Desktop / Cursor / any MCP client

What works today / 现在能用的

One call:

import { dateContext } from "@icyn/date";

dateContext("2026-02-17", { region: "CN" });
// {
//   date: "2026-02-17", region: "CN",
//   civil:    { weekday: 2, isoWeek: 8, isoWeekYear: 2026, dayOfYear: 48, leapYear: false },
//   workday:  { available: true, kind: "public_holiday", isWorkday: false, confidence: "certain", source: "official",
//               holiday: { id: "spring-festival", festival: "lunar-new-year", name: { "zh-Hans": "春节", en: "Chinese New Year" }, dayIndex: 3, span: 9 },
//               meta: { region: "CN", data_version: "2026.09.18", verified_until: 2026, … } },
//   lunar:    { year: 2026, month: 1, day: 1, yearGanZhi: "丙午", zodiac: "马", monthName: "正月", dayName: "初一", … },
//   solarTerm:{ onThisDay: null, current: { name: { zh: "立春", en: "Beginning of Spring" }, at: "2026-02-03T20:01:51.000Z" }, next: { zh: "雨水", … } }
// }

Dates can be given as "2026-02-17", [2026, 2, 17], { year, month, day } or a Date (UTC fields). Every holiday answer carries source (official / baseline / predicted), confidence (certain / likely / uncertain) and data version metadata; a year we know nothing about comes back as { available: false, reason }, never a guess.

Pieces:

import { solarToLunar, lunarToSolar } from "@icyn/date";

solarToLunar("2026-02-17");
// { year: 2026, month: 1, day: 1, leap: false, yearGanZhi: "丙午", dayGanZhi: "…",
//   zodiac: "马", monthName: "正月", dayName: "初一", isLeapYear: false, monthLength: 30 }

lunarToSolar({ year: 2033, month: 11, day: 1, leap: true }); // [2033, 12, 22]

import { solarTerms, solarTermAt, solarTermOnDay } from "@icyn/date";
solarTermOnDay("2026-02-04");          // { name: { zh: "立春", en: "Beginning of Spring" }, at: 2026-02-03T20:01:51Z, … }
solarTermAt(new Date());               // { current, next } with exact instants
solarTerms(2027);                      // all 24 of the year

import { dayInfo, nextWorkday, workdaysBetween, holidays } from "@icyn/date";
dayInfo("2026-02-14", "CN");           // { kind: "adjusted_workday", isWorkday: true, source: "official", confidence: "certain", … }
dayInfo("2027-02-13", "CN");           // { kind: "weekend", source: "predicted", confidence: "uncertain", note: "Within the usual 调休 window…" }
regionsObserving("lunar-new-year", 2026); // [{ region: "HK", days: [...] }, { region: "KR", … }, …]
dayInfo("2026-01-06", "DE-BY");        // Heilige Drei Könige — subdivision holiday, resolvedRegion "DE-BY"
nextLongWeekend("CN", "2026-09-18", 7); // { start: "2026-10-01", end: "2026-10-07", days: 7 }
nextLunarDate(8, 15, "2026-09-18");    // next 中秋: { date: "2026-09-25", lunarYear: 2026, adjusted: false }
describe("2026-02-17", { region: "CN" });
// "2026-02-17 星期二，农历丙午马年正月初一，CN 放假：春节（第 3/9 天）。"
nextWorkday("CN", "2026-09-30");       // "2026-10-08"
workdaysBetween("CN", "2026-02-13", "2026-02-24");

• Solar ⇄ lunar for every day 1900-01-31 .. 2100-12-31 (MAX_DATE; that last date falls inside lunar 2100 腊月, so monthLength for that month is null — the table ends mid-month and the real length is unknown)
• Year / day 干支, zodiac, Chinese month & day names, leap month handling (incl. the 2033 閏冬月 case)
• 24 solar terms as exact instants (second precision), current/next lookup, "is there a term on this day" at any UTC offset
• Workday / holiday queries for 12 regions, every answer tagged official / baseline / predicted — never silently guessed
• Zero dependencies, no runtime astronomy; ~480 KB of table data, of which only the lunar/solar-term tables and CN are in the default entry point — the other 11 regions and their 70+ subdivisions load only if you import them

Error model / 失败行为

• Functions that return an info object (dayInfo, dateContext, holidays) never throw for missing data: they return { available: false, reason } or an empty list.
• Functions that return a scalar (isWorkday, addWorkdays, nextWorkday, workdayCount) throw RangeError when the region-year is not covered.
• Search functions (nextLongWeekend, nextLunarDate) return null when nothing is found in range, and throw when data runs out.
• Bad input (unknown region, malformed date, 2 月 30 日) always throws TypeError / RangeError. Region codes are case-insensitive ("us-ca" = "US-CA"); a code with no data at all still throws.
• Prediction is forward-only. A year we have not entered is extrapolated only if it is after the last entered year (coverage(region).predictedFrom). Past uncovered years return { available: false } rather than a guess — extrapolating the current 《放假办法》 backwards would invent history (清明/端午/中秋 became statutory only in 2008, 春节 runs 除夕..初三 only from 2025).

How it is verified / 验证方式

tools/gen_fixtures.py and tools/gen_solar_terms.py generate fixtures/lunar-1900-2100.json (73,384 rows) from two independent reference implementations (sxtwl, lunar_python). The test suite converts every row in both directions. Anything the two references disagree on is written to fixtures/lunar-disagreements.json and adjudicated by hand (see NOTES.md). A release is blocked unless 100% of rows pass.

npm install
npm test                 # Node only

# the full release gate: build + tsc + tests + the CN cross-check
python3 -m pip install -r tools/requirements.txt   # one pure-Python package
npm run check

The last step of npm run check verifies CN.json day-by-day against chinesecalendar. If that package is missing it fails loudly rather than skipping — an unverified table must not look like a passing gate.

Roadmap / 路线图

• [x] Lunar core + 1900–2100 fixtures
• [x] 24 solar terms with exact instants (two references agree within 55 s; spot-check against 紫金山天文台 published values before release)
• [x] Holidays CN 2024–2026 official (incl. 调休), cross-checked day-by-day with chinesecalendar; later years → statutory days predicted from lunar/solar-term rules (forward-only; earlier years are never guessed)
• [x] Holidays HK/MO/TW/JP/KR/VN/SG/US/GB/DE/FR 2024–2028 as baseline (python-holidays rules), CNY dates cross-checked against our lunar table
• [x] Region time zones (DST-aware via Intl) so JP/KR/EU decide solar-term days in their own zone; region hierarchy (US-CA, DE-BY, GB-SCT, 70+ subdivisions as diffs); holiday kind (public/federal/bank/substitute); previousWorkday / addWorkdays / workdayCount / holidaysBetween / isHolidayEve / nextLongWeekend; month & hour 干支, nextLunarDate (lunar birthdays); describe() one-sentence zh/en output for MCP
• [x] dateContext() one-call API, canonical date input, confidence levels, BCP-47 names with guaranteed en + zh-Hans, canonical festival ids across regions, data version metadata, graceful available: false
• [ ] Upgrade baseline regions to official year by year against gazettes (TW 補班, HK gazette, KR substitute days first)
• [ ] "On this day" from Wikipedia (CC BY-SA, attributed per entry)
• [x] @icyn/date npm package (esbuild ESM, per-region entry points, d.ts) · @icyn/date-mcp MCP server (11 tools, stdio, smoke-tested end to end)
• [ ] icyndate pip package (same test vectors)
• [ ] Hosted API

Repository layout / 目录

docs/        product & technical plan（产品与技术方案）, worklog
fixtures/    reference test vectors (generated, committed)
tools/       fixture generators (Python, not shipped)
packages/core/  @icyn/date — the library
packages/mcp/   @icyn/date-mcp — MCP server

License

MIT for code and the derived lunar / solar-term tables. The baseline holiday tables for the eleven non-CN regions are derived from python-holidays (MIT) — its licence is reproduced in THIRD-PARTY-LICENSES, and each generated file records the exact version in baseline_note. Other third-party data (Wikipedia, government holiday notices) keeps its own licence and is attributed per entry.