What is a cron job collision?

A cron collision happens when two or more scheduled jobs fire in the exact same minute. Both processes compete for CPU, memory, disk I/O, or the same database tables at once, which can degrade performance or fail jobs outright.

Can overlapping cron jobs cause database deadlocks?

Yes. If two concurrent jobs write to the same tables — for example a nightly backup and a sync engine both starting at 02:00 — they can hold conflicting locks and deadlock, or exhaust the connection pool. Staggering start minutes is the standard fix.

How do I stagger cron jobs to avoid overlap?

Offset the minute field so heavy jobs never share a start minute: move "0 2 * * *" to "10 2 * * *", or replace "*/15" with an offset step like "7-59/15". Re-simulate after each change until the collision banner reports a clean schedule.

Does this tool upload my crontab anywhere?

No. The parser and the 1,440-minute simulation matrix run entirely in your browser with vanilla JavaScript. Nothing is sent to a server, stored, or tracked.

/tools/cron-overlap-tracker

Cron Overlap & Collision Matrix

Paste raw crontab -l lines and simulate a rolling 24-hour window minute-by-minute. Jobs that fire in the same minute block are flagged as collision risks — before they deadlock your database at 2:00 AM.

Crontab input workspace

One job per line. Prefix a line with # Name to label the job below it.

Simulation day

24-hour load timeline

clear (≤1 job/minute)
2 concurrent
▲ 3+ concurrent

Narrative log

The chronological collision narrative renders here after simulation.

JavaScript is required to run the client-side simulation engine. The sample crontab above shows the expected input format.

Crontab input workspace

Simulation output

24-hour load timeline

Narrative log