The cron expression for every 12 hours

To run a job every 12 hours, use 0 */12 * * *. Read aloud it means: At minute 0 past every 12th hour.

Field by field: minute 0 — minute 0; hour */12 — every 12th hour; day of month * — every day-of-month; month * — every month; day of week * — every day-of-week.

Drop the expression into a crontab, a CI schedule, or anything else that speaks standard five-field cron syntax. The times above are in your local timezone — most cron daemons run in the server's timezone, so mind the difference when it matters.