Cron parse, humanize and next N runs

$0.005 USDC per call · Business, finance and compliance · POST /api/v1/cron-explain · Id cron-explain

Parses a POSIX 5-field or Quartz 6/7-field cron expression (plus macros @yearly/@monthly/@weekly/@daily/@hourly), returns a plain-English summary and the next N scheduled runs in a given IANA timezone, and reports if the expression never fires or lands on a DST-ambiguous wall-clock. Handles step syntax, named months and days, Quartz '?'/L/W/# extensions, and the POSIX dom-OR-dow rule when both fields are restricted. Deterministic: no clock, no model; the `after` parameter is the anchor so output is reproducible.

What you get

Cron bugs ship silently until the job misses; this gives the same reading of the expression a reliable scheduler would, before deploy.

Call it

Send the JSON body below to https://agents.writerslogic.com/api/v1/cron-explain. An unpaid request answers 402 with the price and how to pay; a request that fails with a 5xx status is not charged.

curl -i -X POST https://agents.writerslogic.com/api/v1/cron-explain \
  -H 'content-type: application/json' \
  -d '{"expression":"0 0 29 2 *","timezone":"UTC","after":"2024-02-29T01:00:00Z","count":3}'

Input

Field	Type	Required	Description
`expression`	string; length 0..200	yes	The cron expression or macro, e.g. '/15 9-17 * 1-5' or '@weekly'.
`flavor`	string; one of "posix", "quartz"	no	Which cron dialect. Defaults to posix (5 fields) or quartz (6/7 fields) based on token count.
`timezone`	string; length 0..60	no	IANA timezone name, e.g. 'America/Los_Angeles'. Defaults to UTC.
`after`	string; length 0..40	no	ISO-8601 instant: find runs strictly after this. Defaults to 1970-01-01T00:00:00Z.
`count`	integer	no	How many future runs to return, 1-50. Default 5.

Example request body

{
  "expression": "0 0 29 2 *",
  "timezone": "UTC",
  "after": "2024-02-29T01:00:00Z",
  "count": 3
}

Result

The response is { "data": ..., "_provenance": ... }. data carries these fields; _provenance is a signed W3C Verifiable Credential with a C2PA-style manifest, checked free at POST /api/v1/verify-provenance.

Field	Type	Required	Description
`status`	string; one of "pass", "fail", "unknown", "unsupported"	no	pass: every rule held. fail: a rule was violated (see witnesses). unknown: the input lacks the evidence to decide. unsupported: outside what this engine covers. Missing evidence is never a pass.
`expression`	string	no
`valid`	boolean	no
`flavor`	string	no
`humanized`	string	no
`timezone`	string	no
`runs`	array<string>	no	Next N occurrences as ISO-8601 instants.
`neverFires`	boolean	no
`ambiguousDst`	array<string>	no	Runs that land in a wall-clock interval that occurs twice (fall-back) or not at all (spring-forward).
`witnesses`	array<object>	no
`versions`	object	no	Every semantic dependency of this answer (engine, tables and their as-of dates, tokenizer, calendar, rounding profile).
`limits`	array<string>	no
`deterministic`	boolean	no	Always true: pure code, no model.

Pay and connect

Available through: x402 (USDC on Base), MCP. MCP clients reach it through the calendar-deadline-kit package.

Machine-readable

This agent as JSON (schemas, example, OpenAPI operation)
Free signed sample response
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