cRonstrue

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cRonstrue is a JavaScript library that parses a cron expression and outputs a human readable description of the cron schedule. For example, given the expression "/5 *" it will output "Every 5 minutes".

This library was ported from the original C# implementation called cron-expression-descriptor and is also available in a few other languages.

Features

Zero dependencies
Supports all cron expression special characters including * / , - ? L W, #
Supports 5, 6 (w/ seconds or year), or 7 (w/ seconds and year) part cron expressions
Quartz Job Scheduler cron expressions are supported
i18n support with 30+ languages

Demo

A demo is available here.

Installation

cRonstrue is exported as an UMD module so it will work in an AMD, CommonJS or browser global context.

First, install the module:

npm install cronstrue

Then, depending upon your usage context, add a reference to it:

Node / CommonJS

const cronstrue = require('cronstrue');

ESM / webpack / TypeScript

import cronstrue from 'cronstrue';

Browser

The cronstrue.min.js file from the /dist folder in the npm package should be served to the browser. There are no dependencies so you can simply include the library in a <script> tag.

<script src="https://github.com/bradymholt/cRonstrue/raw/main/cronstrue.min.js" type="text/javascript"></script>
<script>
  var cronstrue = window.cronstrue;
</script>

CDN

A simple way to load the library in a browser is by using the unpkg CDN, which is a "fast, global content delivery network for everything on npm". To use it, include a script tag like this in your file:

<script src="https://unpkg.com/cronstrue@latest/dist/cronstrue.min.js" async></script>

Using the "latest" tag will result in a 302 redirect to the latest version tag so it is recommended to use a specific version tag such as https://unpkg.com/cronstrue@1.48.0/dist/cronstrue.min.js to avoid this redirect.

Usage

cronstrue.toString("* * * * *");
> "Every minute"

cronstrue.toString("0 23 ? * MON-FRI");
> "At 11:00 PM, Monday through Friday"

cronstrue.toString("0 23 * * *", { verbose: true });
> "At 11:00 PM, every day"

cronstrue.toString("23 12 * * SUN#2");
> "At 12:23 PM, on the second Sunday of the month"

cronstrue.toString("23 14 * * SUN#2", { use24HourTimeFormat: true });
> "At 14:23, on the second Sunday of the month"

cronstrue.toString("* * * ? * 2-6/2", { dayOfWeekStartIndexZero: false });
> "Every second, every 2 days of the week, Monday through Friday"

cronstrue.toString("* * * 6-8 *", { monthStartIndexZero: true });
> "Every minute, July through September"

cronstrue.toString("@monthly");
> "At 12:00 AM, on day 1 of the month"

For more usage examples, including a demonstration of how cRonstrue can handle some very complex cron expressions, you can reference the unit tests.

CLI Usage

$ npm install -g cronstrue

$ cronstrue 1 2 3 4 5
At 02:01 AM, on day 3 of the month, and on Friday, only in April

$ cronstrue 1 2 3
Error: too few arguments (3): 1 2 3
Usage (5 args): cronstrue minute hour day-of-month month day-of-week
or
Usage (6 args): cronstrue second minute hour day-of-month month day-of-week
or
Usage (7 args): cronstrue second minute hour day-of-month month day-of-week year

Options

An options object can be passed as the second parameter to cronstrue.toString. The following options are available:

throwExceptionOnParseError: boolean - If exception occurs when trying to parse expression and generate description, whether to throw or catch and output the Exception message as the description. (Default: true)
verbose: boolean - Whether to use a verbose description (Default: false)
dayOfWeekStartIndexZero: boolean - Whether to interpret cron expression DOW 1 as Sunday or Monday. (Default: true)
monthStartIndexZero: boolean - Wether to interpret January as 0 or 1. (Default: false)
use24HourTimeFormat: boolean - If true, descriptions will use a 24-hour clock (Default: false but some translations will default to true)
locale: string - The locale to use (Default: "en")
tzOffset: number - Your time offset (in hours) from UTC (Default: 0)

i18n

To use the i18n support cRonstrue provides, you can either import all the supported locales at once (using cronstrue/i18n) or import individual locales (using cronstrue/locales/[locale]). Then, when calling toString you pass in the name of the locale you want to use. For example, for the es (Spanish) locale, you would use: cronstrue.toString("* * * * *", { locale: "es" }).

All Locales

You can import all locales at once with cronstrue/i18n. This approach has the advantage of only having to load one module and having access to all supported locales. The tradeoff with this approach is a larger module (~130k, minified) that will take longer to load, particularly when sending down to a browser.

// Node / CommonJS
const cronstrue = require('cronstrue/i18n');

// ESM / webpack / TypeScript
import cronstrue from 'cronstrue/i18n';

// Browser
<script src="https://unpkg.com/cronstrue@latest/cronstrue-i18n.min.js" async></script>

cronstrue.toString("*/5 * * * *", { locale: "fr" }); // => Toutes les 5 minutes
cronstrue.toString("*/5 * * * *", { locale: "es" }); // => Cada 5 minutos

Individual Locales

You can also load the main cronstrue module and then load individual locale modules you want to have access to. This works well when you have one or more locales you know you need access to and want to minimize load time, particularly when sending down to a browser. The main cronstrue module is about 42k (minified) and each locale is about 4k (minified) in size.

// Node / CommonJS
const cronstrue = require('cronstrue');
require('cronstrue/locales/fr');
require('cronstrue/locales/es');

// ESM / webpack / TypeScript
import cronstrue from 'cronstrue';
import 'cronstrue/locales/fr';
import 'cronstrue/locales/es';

// Browser
<script src="https://unpkg.com/cronstrue@latest/dist/cronstrue.min.js" async></script>
<script src="https://unpkg.com/cronstrue@latest/locales/fr.min.js" async></script>
<script src="https://unpkg.com/cronstrue@latest/locales/es.min.js" async></script>

cronstrue.toString("*/5 * * * *", { locale: "fr" }); // => Toutes les 5 minutes
cronstrue.toString("*/5 * * * *", { locale: "es" }); // => Cada 5 minutos

Frequently Asked Questions

The cron expression I am passing in is not valid and this library is giving strange output. What should I do?

This library does not do full validation of cron expressions and assumes the expression passed in is valid. If you need to validate an expression consider using a library like cron-parser. Example validation with cron-parser:

const cronParser = require("cron-parser");
const cronstrue = require("cronstrue");

const expression = "* * * * * *";

// Validate expression first
let isCronValid = true;
try { cronParser.parseExpression(expression) } catch(e) { isCronValid = false; }

// If valid, then pass into cRonstrue
if (isCronValid) {
 console.log(cronstrue.toString("* * * * *"));
}

Can cRonstrue output the next occurrence of the cron expression?

No, cRonstrue does not support this. This library simply describes a cron expression that is passed in.