Universally Unique Lexicographically Sortable Identifier

ULIDs are unique, sortable identifiers that work much in the same way as UUIDs, though with some improvements:

• Lexicographically sortable
• Canonically encoded as a 26 character string, as opposed to the 36 character UUID
• Uses Crockford's base32 for better efficiency and readability (5 bits per character)
• Monotonic sort order (correctly detects and handles the same millisecond)

ULIDs also provide:

• 128-bit compatibility with UUID
• 1.21e+24 unique IDs per millisecond
• Case insensitivity
• No special characters (URL safe)

UUID can be suboptimal for many uses-cases because:

• It isn't the most character efficient way of encoding 128 bits of randomness
• UUID v1/v2 is impractical in many environments, as it requires access to a unique, stable MAC address
• UUID v3/v5 requires a unique seed and produces randomly distributed IDs, which can cause fragmentation in many data structures
• UUID v4 provides no other information than randomness which can cause fragmentation in many data structures

Installation

Install using NPM:

npm install ulid --save

Compatibility

ULID supports the following environments:

Additionally, both ESM and CommonJS entrypoints are provided.

Usage

To quickly generate a ULID, you can simply import the ulid function:

import { ulid } from "ulid";

ulid(); // "01ARZ3NDEKTSV4RRFFQ69G5FAV"

Seed Time

You can also input a seed time which will consistently give you the same string for the time component. This is useful for migrating to ulid.

ulid(1469918176385) // "01ARYZ6S41TSV4RRFFQ69G5FAV"

Monotonic ULIDs

To generate monotonically increasing ULIDs, create a monotonic counter with monotonicFactory.

Note that the same seed time is being passed in for this example to demonstrate its behaviour when generating multiple ULIDs within the same millisecond

import { monotonicFactory } from "ulid";

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"

Pseudo-Random Number Generators

ulid automatically detects a suitable (cryptographically-secure) PRNG. In the browser it will use crypto.getRandomValues and on NodeJS it will use crypto.randomBytes.

Using Math.random (insecure)

By default, ulid will not use Math.random to generate random values. You can bypass this limitation by overriding the PRNG:

const ulid = monotonicFactory(() => Math.random());

ulid(); // "01BXAVRG61YJ5YSBRM51702F6M"

Validity

You can verify if a value is a valid ULID by using isValid:

import { isValid } from "ulid";

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

ULID Time

You can encode and decode ULID timestamps by using encodeTime and decodeTime respectively:

import { decodeTime } from "ulid";

decodeTime("01ARYZ6S41TSV4RRFFQ69G5FAV"); // 1469918176385

Note that while decodeTime works on full ULIDs, encodeTime encodes only the time portion of ULIDs:

import { encodeTime } from "ulid";

encodeTime(1469918176385); // "01ARYZ6S41"

Tests

Install dependencies using npm install first, and then simply run npm test to run the test suite.

CLI

ulid can be used on the command line, either via global install:

npm install -g ulid
ulid

Or via npx:

npx ulid

You can also generate multiple IDs at the same time:

ulid --count 15

Specification

You can find the full specification, as well as information regarding implementations in other languages, over at ulid/spec.

Performance

You can test ulid's performance by running npm run bench:

Simple ulid x 56,782 ops/sec ±2.50% (86 runs sampled)
ulid with timestamp x 58,574 ops/sec ±1.80% (87 runs sampled)
Done!