Cron Monitor

Description

WordPress runs background tasks, called cron jobs, for things like publishing scheduled posts,
sending emails and running backups. It keeps no record of them, so when one fails or stops you
never find out.

Cron Monitor keeps that record. It shows what ran, what failed and which plugin is behind each
job, and it tells you when something goes wrong.

Features

• Run history: every job that ran, how long it took and whether it worked.
• Catches crashes: fatal errors and timeouts are recorded too.
• Plugin owner: see which plugin or theme created each job.
• Safe cleanup: finds jobs left behind by deleted plugins and tells you which are safe to delete.
• Duplicate finder: spots jobs scheduled twice and removes the extras, with a preview first.
• Health check: a list of cron problems on your site, most important first.
• Alerts: email, Slack or Discord when a job crashes, runs late or stops running.
• Manage jobs: add, edit, run now, pause or delete any scheduled job.
• Pause a job: stop one job without turning off the plugin that owns it.
• Custom schedules: create your own intervals, like every 10 minutes.
• Fixed time of day: keep a daily job at 03:00, even when the clocks change.
• What changed: see which jobs appeared or disappeared in the last week.
• WooCommerce: logs failed Action Scheduler tasks.
• CSV export: download jobs and run history.
• Developer tools: WP-CLI commands and a REST API (see Technical details below).

Good to know

• Alerts are off until you turn them on.
• Nothing is sent to anyone but you. No tracking, no ads.
• Deleting the plugin removes everything it created.

Technical details

WP-CLI

• wp cronmon runs: recorded runs. Filters: --hook, --status, --since, --limit.
• wp cronmon health: the Cron Health findings. Exits non-zero when one is critical.
• wp cronmon orphans: every event with its safe-to-delete verdict.

All three accept --format=json.

REST API

Both routes require manage_options. Use Application Passwords over HTTPS.

• GET /wp-json/cronmon/v1/health: the Cron Health findings, a critical count and an ok
  boolean for Uptime Kuma, Zabbix, Better Stack and similar monitors.
• GET /wp-json/cronmon/v1/runs?status=fatal&since=-1%20hour&limit=20: recorded runs. Timestamps
  are ISO 8601 UTC.

Logging from your own code

Inside a cron callback, attach a note to the current run:

do_action( 'cronmon_log', 'reindexed 412 products' );

With Cron Monitor inactive, the call does nothing.

Server cron setup

Add to wp-config.php:

define( 'DISABLE_WP_CRON', true );

Then add a system cron entry, every five minutes:

*/5 * * * * cd /path/to/wordpress && wp cron event run --due-now > /dev/null 2>&1

Or, without WP-CLI:

*/5 * * * * wget -q -O - https://example.com/wp-cron.php?doing_wp_cron > /dev/null 2>&1

Cron Monitor never writes to wp-config.php.

How it works

• A run is recorded when it starts, not when it finishes, so crashes and timeouts still leave a
  record.
• Cron Monitor attaches itself to every scheduled hook, so a hook with no callbacks now fires and
  is recorded as “0 callbacks”. Nothing else changes.
• Duplicates are matched on hook, arguments and schedule together. One-off events are never
  removed automatically.
• Late-running cron is traced to the job that held the cron lock too long, and a
  WP_CRON_LOCK_TIMEOUT value is recommended.

Performance

• Front-end page views load two small PHP files and run no queries. With alerts on, one or two
  queries are added unless you have a persistent object cache.
• Each cron job adds two database writes, one when it starts and one when it finishes.
• Measured instrumentation cost is about 0.005 ms and 2.7 KB per cron job (PHP 8.4, one machine).

What this plugin stores

Two database tables per site:

• cronmon_runs: one row per run. Hook name, an md5 hash of the arguments (never the values),
  timing, memory, query count, outcome, and the first error message (up to 2,000 characters).
• cronmon_hooks: one row per scheduled event, with the callbacks last seen on it and who owns
  them.

Settings live in the cronmon_settings option. The stopped-running check uses one transient and
one small option. Successful runs are kept for 7 days and failures for 14, capped at 50,000 rows.
All of it is removed on uninstall.

No third-party libraries are bundled and nothing is minified.

External services

This plugin contacts no third-party service of its own. No analytics, no update checker. It makes
at most two kinds of outbound request, both under your control:

• Alert webhook (optional, off by default): sent to the URL you enter, typically Slack or
  Discord. The JSON body contains the hook name, event type, start time, duration and, for a
  failure, the truncated error message.
• Loopback check: the Cron Health screen, Site Health test and REST health route can ask your
  own wp-cron.php whether it answers. This goes to your own site_url(). It never runs during
  cron or WP-CLI, is cached for an hour, and is skipped where something else manages cron
  (Cavalcade, Cron Control, DISABLE_WP_CRON, ALTERNATE_WP_CRON).

Alert emails are sent through wp_mail() to the address you enter, using your site’s own mail
setup.

Technical details