UUID generator

What this UUID generator does

Click once and get up to 100 fresh version 4 UUIDs, each produced by the browser’s crypto.randomUUID(). They are lowercase, hyphenated, 36 characters long and ready to paste into a database seed, a test fixture, a config file or an API request. Every ID can be copied on its own, or the whole list can be copied newline-separated. Generation is instant and local.

How to use it

1. Set Count (1–100; the page starts with 5).
2. Click Generate. Each click replaces the list with new values.
3. Click Copy next to a single ID, or Copy all to grab the list, one UUID per line.

The input is clamped: 0 or a negative number produces one UUID, anything above 100 produces 100.

Anatomy of a v4 UUID

f47ac10b-58cc-4372-a567-0e02b2c3d479
│        │    │    │    └─ 12 hex (48 bits) random
│        │    │    └─ variant: first digit is 8, 9, a or b
│        │    └─ version: always 4 here
│        └─ 4 hex (16 bits) random
└─ 8 hex (32 bits) random

The groups are 8-4-4-4-12 hex digits = 32 hex digits = 128 bits, with 4 hyphens making 36 characters. Only two positions are fixed (the version nibble and the variant bits), which is how a regex like ^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$ can validate a v4 UUID. The all-zero 00000000-0000-0000-0000-000000000000 is the “nil” UUID and is never produced by a generator.

UUID versions compared

Version	Built from	Sortable by time	Leaks	When to prefer it
v1	60-bit timestamp + clock sequence + MAC address	Roughly (byte order is awkward)	MAC address and creation time	Legacy systems only
v4	122 random bits	No	Nothing	Tokens, tests, keys where order does not matter
v5	SHA-1 of a namespace + name	No	Nothing (deterministic)	Stable IDs derived from a URL or name
v7	48-bit Unix millisecond timestamp + 74 random bits	Yes, lexically and in binary	Creation time	Database primary keys, event logs, anything indexed

This tool generates v4 only. If you need v7 in code, the uuid npm package (uuidv7()), PostgreSQL 18’s uuidv7() and many ORMs provide it.

UUIDs as database keys

A random v4 key is fine until the table is large enough that the index no longer fits in memory. Because each new key is uniformly random, inserts touch random index pages, causing page splits and cache misses; v7 keys are monotonically increasing so inserts append. Practical rules:

• Store as 16 bytes, not 36 characters. Postgres has a native uuid type; MySQL and SQL Server use BINARY(16) / UNIQUEIDENTIFIER. Text storage more than doubles index size.
• Do not strip the hyphens in APIs and logs; every parser expects them, and the compact 32-char form is a different representation.
• Use v4 when the ID is public and creation time is sensitive (invite links, unsubscribe tokens). v7 reveals when the row was created, down to the millisecond.
• Do not use a UUID as a secret on its own for anything long-lived — it is unguessable, but it is not a replacement for authentication.

Generating UUIDs in code

const id = crypto.randomUUID(); // browser (secure context) and Node 19+

In Node 14–18 use import { randomUUID } from 'node:crypto'. On the command line, uuidgen (macOS, Linux) or PowerShell’s [guid]::NewGuid() produce v4 values; Linux also exposes /proc/sys/kernel/random/uuid.

Related tools and snippets

• Hash generator — a v5 UUID is a SHA-1 hash of a name; see what the raw digest looks like.
• Timestamp converter — decode the millisecond timestamp at the front of a v7 UUID.
• Number base converter — read the hex groups of a UUID as decimal or binary.
• Lorem ipsum generator — the other half of a test fixture: placeholder text to go with the IDs.
• JWT decoder — UUIDs commonly fill the jti and sub claims.