Cron Expression Generator

Create Linux crontab expressions for hourly, daily, weekly, monthly and custom recurring schedules.

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// about

About this Tool

Cron uses five fields to describe when a Linux command should run. This generator turns familiar recurring schedule choices into a ready-to-copy expression.

How to use it

  1. Choose how often the job repeats.
  2. Select the time and calendar values shown for that schedule.
  3. Copy the generated expression and place it before your shell command.

Why people use this tool

  • Useful when cron syntax is difficult to remember.
  • Creates standard five-field Linux crontab expressions.
  • Copy the result directly into a crontab file or deployment script.
Guides · Date & time · 7 min read

Unix Timestamps Explained: Seconds vs Milliseconds, Time Zones and the Year 2038 Problem

When is 1700000000? Why do some systems use 13-digit numbers? Why is the time off by exactly nine hours? Most time bugs disappear once you understand a few concepts.

A Unix timestamp (Unix time, epoch time) is a single integer counting the seconds elapsed since 00:00:00 UTC on 1 January 1970, the Unix epoch. 0 is 1970-01-01 00:00:00 UTC and 1700000000 is 2023-11-14 22:13:20 UTC.

0           → 1970-01-01 00:00:00 UTC
1700000000  → 2023-11-14 22:13:20 UTC
1735689600  → 2025-01-01 00:00:00 UTC
2147483647  → 2038-01-19 03:14:07 UTC
What a Unix timestamp is, how to tell 10-digit from 13-digit values, converting between UTC and local time, daylight saving pitfalls and the 2038 problem.
Read guide →

Related guides

Date & time 6 min read

How to Read and Write Cron Expressions: The Five Fields and Common Examples

What each of the five cron fields means, how to use *, /, - and commas, common schedules, and the pitfalls around day fields and time zones.

Read guide
Build it with AI

Build this tool yourself with AI

Want your own version of this tool? Copy the work-order prompt into an AI chat, or save the skill file for an AI coding agent. Both describe the features, edge cases and test cases we used when building it.

AI work-order prompt

Paste it as-is into an AI chat such as Claude, ChatGPT or Gemini.

You are an experienced full-stack web developer. Build a web tool called "Cron Expression Generator" that meets the requirements below.

## Goal

Build a tool that creates and explains standard five-field cron expressions from a chosen schedule.

## Core features

- Schedule picker (every N minutes, hourly, daily, weekly, monthly)
- Plain-language description of the expression
- Preview of the next five run times
- Time zone selection (UTC, Asia/Seoul, …)
- Parse an expression typed by the user

## Inputs

- Schedule type and minute/hour/weekday/day values
- Time zone

## Outputs

- Cron expression
- Description
- Next run times

## Edge cases and handling rules

- Warn that setting both day fields means OR
- Explain steps that do not divide evenly, such as */45
- Validate out-of-range values like minute 60
- Explain run-time differences on UTC servers

## Implementation requirements

- Build it as a single page (HTML, CSS, JavaScript) that runs entirely in the browser, and never send the user's input to a server.
- Make the UI responsive and easy to use on mobile; label every input and keep everything keyboard accessible.
- Add a Copy button for results and show clear, friendly error messages for invalid input.
- Keep the core logic in functions separate from the UI so it can be unit-tested.

## Definition of done (test cases)

- Daily at 02:00 gives '0 2 * * *'
- Weekdays at 09:30 give '30 9 * * 1-5'
- '*/15 * * * *' runs every 15 minutes

First outline your implementation plan in at most five lines, then write the complete code, and finally explain how to check the test cases above.

Skill (SKILL.md)

Save it as .claude/skills/build-cron-generator/SKILL.md for AI coding agents such as Claude Code to reuse whenever you build or change this tool.

---
name: build-cron-generator
description: Use when building or changing a Cron Expression Generator tool. Build a tool that creates and explains standard five-field cron expressions from a chosen schedule.
---

# Build: Cron Expression Generator

## Goal

Build a tool that creates and explains standard five-field cron expressions from a chosen schedule.

## Workflow

1. Review the required features, inputs and outputs below and ask about anything missing first.
2. Implement the core logic as pure functions separate from the UI.
3. Check the logic against the test cases in the verification list.
4. Build a responsive UI with an input form, a result area and a Copy button.
5. Reproduce each edge case listed under Rules and refine the error messages.

## Core features

- Schedule picker (every N minutes, hourly, daily, weekly, monthly)
- Plain-language description of the expression
- Preview of the next five run times
- Time zone selection (UTC, Asia/Seoul, …)
- Parse an expression typed by the user

## Inputs

- Schedule type and minute/hour/weekday/day values
- Time zone

## Outputs

- Cron expression
- Description
- Next run times

## Rules

- Warn that setting both day fields means OR
- Explain steps that do not divide evenly, such as */45
- Validate out-of-range values like minute 60
- Explain run-time differences on UTC servers
- Build it as a single page (HTML, CSS, JavaScript) that runs entirely in the browser, and never send the user's input to a server.

## Verification

- [ ] Daily at 02:00 gives '0 2 * * *'
- [ ] Weekdays at 09:30 give '30 9 * * 1-5'
- [ ] '*/15 * * * *' runs every 15 minutes

Tips for working with AI

  • Tell the AI your stack (for example React, Vue or plain HTML) on the first line so the code matches your project.
  • Ask it to run the listed test cases and show the results before you accept the code.
  • Never paste real secrets, customer data or API keys into the prompt; use sample values instead.