Why scheduled posts don't publish on time — inspecting WP-Cron with WP-CLI

A post scheduled to publish at a specific time doesn't go live when expected. A plugin's recurring email notification never arrives. This tends to happen on low-traffic sites, and there's a specific reason for it.

Note: WP-Cron is WordPress’s built-in scheduling system. It sounds like the OS-level cron daemon, but the underlying mechanism is quite different.

WordPress’s WP-Cron doesn’t work like a real OS cron daemon. On every page load, WordPress checks whether any scheduled task is past its due time and, if so, runs it. This is what's known as "pseudo-cron" — and its weakness is that nothing runs without a page visit. Schedule a post to publish at 3am on a site with little overnight traffic, and the publish task can sit unexecuted until the next visitor happens to load a page.

WP-CLI lets you look inside this otherwise invisible system and run exactly the task you need, right now.

Listing what's scheduled