Build crontab expressions visually and translate them to plain English.
cron is a time-based job scheduler built into Unix-like operating systems. It reads a configuration file called a "crontab" (cron table) that contains a list of shell commands and the exact times they should run.
The system daemon (background process) wakes up every minute, checks the current time against all the rules in the crontab, and executes the commands for any rules that match exactly. Because it relies on strict string matching rather than complex calendar logic, it is incredibly lightweight and reliable.
A standard cron expression consists of 5 fields separated by spaces:
The number one reason cron jobs fail in modern distributed systems is Timezone mismatch.
A developer writes a cron job to run at 2 AM on their local Mac (PST), pushes it to AWS, and suddenly the job runs at 6 PM. By default, cron daemon evaluates schedules against the server's local system time (which is usually UTC in cloud environments). When building web apps, always schedule your cron jobs in UTC.
What does the cron expression '0 * * * *' mean?
