dsh-cron-parse

Cron expressions power almost every scheduler out there, but a line of stars, slashes, and comma-separated numbers is opaque the moment it leaves the terminal. dsh-cron-parse collapses that ambiguity into one structured API call: pass in a 5-field expression and receive back a valid/invalid flag, a plain-language English description, the fully expanded value list for each of the five fields, and up to ten concrete upcoming run times — so you never have to reverse-engineer the schedule mentally again.

The parser implements classic Vixie semantics faithfully: a day fires when either dayOfMonth or dayOfWeek is satisfied if both are constrained (OR union), or by whichever single field is constrained; with both unconstrained the job runs daily. Every common syntax form is supported — wildcards, every-nth steps, closed ranges, range-with-step, multi-value lists, and case-insensitive month and weekday names. An unsatisfiability pre-check catches impossible combinations like 'Day 30 in February' immediately, and all arithmetic is performed on wall-clock time in the caller-supplied IANA timezone, returning ISO 8601 strings with explicit UTC offsets.

Teams building scheduling dashboards, alerting pipelines, or internal ops tooling will find it a drop-in fit: no build step, zero runtime dependencies, pure ESM. It slots cleanly into Node or browser contexts, and the self-test routine that fires on mount gives you immediate confidence that parsing and scheduling are wired correctly before you take it to production.