Learn

Developer utilities, explained without the paywall

Every article here pairs with a calculator on this site. Concept on the left, math on the right — both cited to primary specifications (IEEE 1003.1, POSIX.1-2017, RFC 3339, RFC 4648, IANA tzdata), both reviewed by a named human.

Scheduling

Cron Expression Syntax — A Developer's Field Guide

POSIX cron is five fields. Quartz adds a sixth. AWS EventBridge requires ? in one of dom or dow. GitHub Actions runs UTC only. Here is the complete field-level reference with the dialect traps that actually bite you in production.

Updated May 23, 2026 · Pairs with /calculators/cron-expression-builder

Time & Date

Unix Timestamps Explained — Epoch, Y2K38, and ISO 8601 vs RFC 3339

A Unix timestamp is the number of non-leap seconds since 1970-01-01T00:00:00Z per POSIX.1-2017 §4.16. Values above 10¹² are milliseconds. The 32-bit signed maximum hits 2038-01-19T03:14:07Z. Here is everything you need to handle them correctly.

Updated May 23, 2026 · Pairs with /calculators/unix-timestamp-converter