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2.3.0 • Public • Published


ULID generator for NodeJS and the browser

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ULID generator library, based off of the original ulid for NodeJS and the browser. ULIDs are Universally Unique Lexicographically Sortable Identifiers. This library adheres to this specification.

The original ulid is no longer maintained, and has several outstanding compatibility-related issues that were never addressed. This library aims to address those and remain compatible in a larger range of environments.


Install using npm by running: npm install ulidx --save.

ulidx provides types and is written entirely in Typescript. It provides both ESM and CommonJS outputs.


Import ulid to generate new ULIDs:

import { ulid } from "ulidx";


Time seed

You can also provide a time seed which will consistently give you the same string for the time component.

This is useful for migrating to ulid.

ulid(1469918176385); // 01ARYZ6S41TSV4RRFFQ69G5FAV

Monotonic ULID factory

To generate monotonically increasing ULIDs, create a monotonic counter using the factory:

import { monotonicFactory } from "ulidx";

const ulid = monotonicFactory();

// Strict ordering for the same timestamp, by incrementing the least-significant random bit by 1
ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVR8
ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVR9
ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVRA
ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVRB
ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVRC

// Even if a lower timestamp is passed (or generated), it will preserve sort order
ulid(100000); // 000XAL6S41ACTAV9WEVGEMMVRD

Decode ULID Time

Import decodeTime to extract the timestamp embedded in a ULID:

import { decodeTime } from "ulidx";

// Extract milliseconds since UNIX Epoch from ULID
decodeTime("01ARYZ6S41TSV4RRFFQ69G5FAV"); // 1469918176385

Validate ULID

Import isValid to check if a string is a valid ULID:

import { isValid } from "ulidx";

isValid("01ARYZ6S41TSV4RRFFQ69G5FAV"); // true
isValid("01ARYZ6S41TSV4RRFFQ69G5FA"); // false

Crockford's Base32 (Typos tolerance and Hyphened ULIDs)

Import fixULIDBase32 to fix typos and remove hyphens in a ULID:

import { fixULIDBase32 } from "ulidx";


Pseudo-Random Number Generation (PRNG)

ulidx will attempt to locate a suitable cryptographically-secure random number generator in the environment where it's loaded. On NodeJS this will be crypto.randomBytes and in the browser it will be crypto.getRandomValues.

Math.random() is not supported: The environment must have a suitable crypto random number generator.


ulidx is compatible with the following environments:

  • NodeJS 16 and up
    • Node REPL
  • Browsers with working crypto / msCrypto libraries
    • Web workers
  • React-Native ¹
  • Edge compute
    • Cloudflare Workers ²
    • Vercel Edge

¹ React-Native is supported if crypto.getRandomValues() is polyfilled. react-native-get-random-values is one such library that should work well with ulidx. It should be imported before ulidx is used.

² ulidx is not fully compatible with Cloudflare Workers due to their problematic stance on getting the current time. It is recommended to only use monotonic factories in this runtime.


ulidx provides browser bundles in both ESM and CommonJS varieties. Importing should be automatic, but you can import them directly:

  • dist/browser/index.js - Browser ESM build
  • dist/browser/index.cjs - Browser CommonJS build

Unlike version 1.x, these browser builds cannot simply be injected into the browser. They must be included in a build system of some kind, like Rollup or Webpack.

Note that you can use the Node-based builds in the browser if you use such an aforementioned tool, but you will need to stub node:crypto to do so. Consider the following example in Webpack using a plugin:

    // ...

    plugins: [
        new NormalModuleReplacementPlugin(/node:/, (resource) => {
            resource.request = resource.request.replace(/^node:/, "");

    // ...

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