MoonCron

MoonCron is a pure MoonBit library and command-line tool for parsing, validating, explaining, and evaluating classic five-field cron expressions.

Project status: early MVP. The core parser and evaluator work, but the public API may still change before the first stable release.

Features

• Classic five-field syntax: minute, hour, day of month, month, day of week
• Wildcards, lists, ranges, and steps: *, ,, -, /
• Month and weekday names such as JAN and MON-FRI
• Common aliases including @hourly, @daily, @weekly, and @monthly
• Structured validation errors
• Time matching and field-jumping next-occurrence calculation
• Vixie-style day-of-month/day-of-week semantics
• Timezone-free Gregorian calendar model
• Bilingual English and Simplified Chinese natural-language explanations
• CLI commands for validation, explanation, and schedule preview
• Tests on Wasm, Wasm GC, JavaScript, and native backends

Quick start

Validate an expression:

moon run cmd/main -- check "*/15 9-17 * * MON-FRI"

Explain an expression in English or Simplified Chinese:

moon run cmd/main -- explain "0 9 * * MON-FRI" en
moon run cmd/main -- explain "0 9 * * MON-FRI" zh

Expected output:

Runs at 09:00 on Monday through Friday.
在09:00执行，适用于星期一至星期五。

List the next three matching times after a civil date-time:

moon run cmd/main -- next "0 9 * * MON-FRI" 2026-08-08T12:00 3

Expected output:

2026-08-10 09:00
2026-08-11 09:00
2026-08-12 09:00

Library example

///|
test "README example" {
  let schedule = parse("*/30 9-17 * * MON-FRI").unwrap()
  let start : CivilDateTime = {
    year: 2026,
    month: 8,
    day: 10,
    hour: 8,
    minute: 45,
  }
  inspect(schedule.next_after(start).unwrap().to_string(), content="2026-08-10 09:00")
  assert_eq(
    schedule.explain_en(),
    "Runs every 30 minutes during hours 9 through 17 on Monday through Friday.",
  )
  assert_eq(
    schedule.explain_zh(),
    "在9时至17时期间每30分钟执行，适用于星期一至星期五。",
  )
}

Supported syntax

Feature	Example	Status
Wildcard	* * * * *	Supported
List	0 9,12,18 * * *	Supported
Range	0 9-17 * * *	Supported
Step	*/15 * * * *	Supported
Named month	0 0 1 JAN *	Supported
Named weekday	0 9 * * MON-FRI	Supported
Aliases	@daily	Supported
Seconds field	0 */5 * * * *	Not supported
Quartz modifiers	L, W, #, ?	Not supported
Time zones / DST	IANA zone names	Not supported in the core MVP

See docs/compatibility.md for precise cron semantics and docs/explanations.md for explanation behavior.

Search performance

next_after skips disallowed months, calendar days, hours, and minutes instead of scanning every civil minute. The optional search_limit_minutes argument remains an exact bound on civil-minute distance, including for sparse annual schedules.

Development

moon fmt --check
moon check --target all --deny-warn
moon test --target all --deny-warn
moon info

Run the standalone example:

moon run examples/basic

Roadmap

• Add richer source-span diagnostics
• Add deterministic cross-implementation test vectors
• Add a small WebAssembly playground
• Publish the package to mooncakes.io after API review

License

Apache-2.0. See LICENSE.