Cron with Seconds (6-Field) Generator & Analyzer

Q: What is a 6-field cron expression?

A 6-field cron expression adds a leading seconds field to the classic five fields. The order becomes second, minute, hour, day-of-month, month and day-of-week. For example, 30 0 9 * * 1-5 means 'at 09:00:30, Monday through Friday'. This format is used by schedulers that need sub-minute precision, such as the popular node-cron library, Spring's @Scheduled (in Quartz-style), and several Go and Java schedulers.

Q: Which schedulers use seconds in cron?

Standard Unix/Linux crontab does NOT support seconds — it only has five fields. The seconds field appears in application-level schedulers: node-cron and node-schedule in Node.js, Spring Scheduler and Quartz in Java, the cron package in Go (robfig/cron), and many others. Always check your scheduler's documentation, because some treat the leading field as seconds while standard crontab would misread the whole expression.

Q: How do I run something every 30 seconds?

Use a step value in the seconds field: */30 * * * * * fires at second 0 and second 30 of every minute — twice a minute. For every 10 seconds use */10, and for every second use * in the seconds field. Be careful with very frequent schedules: a job that runs every second must finish in well under a second or executions will overlap.

Q: Will a 6-field expression work in a normal crontab?

No. If you paste a 6-field expression into a standard Unix crontab, cron will interpret the first field as minutes and shift everything else, producing a completely different (and usually invalid) schedule. For system crontab use the 5-field variant. Only use the seconds field with a scheduler that explicitly documents support for it.

Q: Are the seconds shown in the next-run times accurate?

Yes. This tool computes the next run times down to the exact second, in your browser's local timezone (shown beneath the list). Remember that the machine running the job uses its own timezone, often UTC, so verify that before relying on the precise times.

Build and analyze 6-field cron expressions with a seconds field — the format used by node-cron, Quartz and other application schedulers. Get plain-English explanations and exact next-run times.

Cron Expression

Paste a cron expression to see what it means and when it runs next.

Common schedules

Second

Minute

Hour

Day of Month

Month

Day of Week

Generated Expression

What It Does

This is the seconds-aware variant of the cron tool. It works with 6-field expressions whose first field is seconds, followed by the familiar minute, hour, day-of-month, month and day-of-week. That extra field unlocks sub-minute scheduling — every 5 seconds, every 30 seconds, or at a precise second of a chosen minute — which standard Unix cron cannot express. Paste an expression to get a plain-English description, the next five run times computed to the exact second in your local timezone, and a field breakdown; or switch to Build mode to assemble one from guided dropdowns and presets. Because the seconds field is only understood by application schedulers like node-cron, Spring and Quartz, the tool is designed for those environments rather than the system crontab.

When to Use It

You are configuring node-cron, node-schedule or a Go/Java scheduler that expects a leading seconds field and want to verify the schedule.
You need a job to run every few seconds and want to confirm the exact second-level timing before deploying.
You inherited a 6-field expression and need to know whether the first number is seconds or minutes and what the schedule really does.
You want sub-minute precision that the standard 5-field crontab simply cannot represent.

Worked Examples

*/30 * * * * *

Every 30 seconds — fires at second 0 and second 30 of every minute. The leading */30 is the seconds field; the rest are wildcards.

0 0 9 * * 1-5

At exactly 09:00:00, Monday through Friday. The first 0 pins the seconds, the second 0 the minutes, and 9 the hour.

15 30 8 * * *

Daily at 08:30:15 — a precise second-level daily trigger that a 5-field cron could not express.

*/5 * * * * *

Every 5 seconds, around the clock. Use sparingly: the job must finish in under 5 seconds to avoid overlapping runs.

Features

6-field cron with a dedicated seconds field

Analyze any 6-field expression or build one visually

Plain-English description of the schedule

Next 5 run times computed to the exact second

Field-by-field breakdown including seconds

Step

range and list support in every field

Warnings for overly frequent (every-second) schedules

Common-schedule presets for node-cron style jobs

One-click copy of the generated expression

Fully client-side with no server calls

How to Use

Analyze: paste a 6-field expression (second minute hour day-of-month month day-of-week) and read the description, exact next-run times and warnings. Build: switch to the Build tab, set the seconds field plus the others using dropdowns or presets, then copy the result. The explanation updates live.

Common Mistakes

Pasting a 6-field expression into a system crontab. Unix cron has no seconds field and will misread the whole line — use a scheduler that documents seconds support.
Confusing the first field. In 6-field cron the first number is seconds, not minutes. 30 * * * * * is every minute at second 30, not every 30 minutes.
Scheduling sub-second-impossible work. A job that runs every second but takes longer than a second to finish will overlap or queue up — make frequent jobs fast and idempotent.
Forgetting the server timezone. Like all cron, the actual run time depends on the scheduler's timezone, not the one shown here.

Frequently Asked Questions

What is a 6-field cron expression?

Which schedulers use seconds in cron?

How do I run something every 30 seconds?

Will a 6-field expression work in a normal crontab?

Are the seconds shown in the next-run times accurate?

The seconds field is only supported by application schedulers (node-cron, Quartz, Spring, robfig/cron and similar) — not the standard Unix crontab. All analysis runs locally in your browser.