UUID Generator — v4 and v7

Generate one or hundreds of UUIDs. Version 4 is fully random; version 7 is ordered by creation time.

Version

How many

Uppercase

Hyphens

{Braces}

UUIDs

Ready

What is a UUID?

A UUID (Universally Unique Identifier), called a GUID in Microsoft ecosystems, is a 128-bit ID written as 32 hexadecimal digits in five groups: 8-4-4-4-12, for example 3f2b8c1e-9d4a-4e7b-b1c2-5a6f7e8d9c0b. UUIDs let separate systems create IDs independently — on different servers, phones or browsers — without asking a central database for the next number, and without realistic risk of two being the same.

UUID v4 vs v7

	Version 4	Version 7
Built from	122 random bits	48-bit Unix timestamp (ms) + 74 random bits
Sort order	Random	Sorts by creation time
Database indexes	Inserts scatter across the index	Inserts append near the end — faster and smaller
Reveals creation time	No	Yes, to the millisecond
Best for	Tokens, public IDs, anything that should not leak timing	Primary keys, event IDs, logs

Version 4

Version 7

Built from

122 random bits

48-bit Unix timestamp (ms) + 74 random bits

Sort order

Random

Sorts by creation time

Database indexes

Inserts scatter across the index

Inserts append near the end — faster and smaller

Reveals creation time

Yes, to the millisecond

Best for

Tokens, public IDs, anything that should not leak timing

Primary keys, event IDs, logs

Version 7 was standardised in RFC 9562 (2024), which replaced the original RFC 4122. It is now the recommended choice for database primary keys in PostgreSQL, MySQL and similar systems, because time-ordered keys keep B-tree indexes compact.

How unique is "unique"?

A v4 UUID has 2¹²² possible values, about 5.3 × 10³⁶. You would need to generate roughly 2.7 quintillion (2.7 × 10¹⁸) of them before there is even a 50% chance of a single duplicate. In practice, collisions only happen when the random number generator is broken. This tool uses crypto.getRandomValues, the browser's cryptographically secure source, for every UUID.

Formats

Standard — lowercase with hyphens, as recommended by RFC 9562.

Uppercase — common in Windows, .NET and SQL Server tooling.

No hyphens — a compact 32-character string, handy for file names and URLs.

{Braces} — the registry-style GUID format used in Windows and COM.

UUIDs are generated in your browser and never sent to a server.

Frequently asked questions

Is a GUID the same as a UUID?

Yes. GUID is Microsoft's name for the same 128-bit identifier format. A UUID with uppercase letters and braces is the usual GUID presentation.

Should I use UUID v4 or v7 for database keys?

v7 is usually better for primary keys because new values sort after old ones, which keeps indexes efficient. Use v4 when the ID must not reveal when it was created.

Can two generated UUIDs ever be the same?

In theory yes, in practice no. With 122 random bits, the chance of a duplicate is negligible even across billions of IDs.

Are UUIDs secure tokens?

Random v4 UUIDs are unpredictable when generated with a secure random source, as here, but dedicated tokens with more randomness are better for secrets such as password-reset links. Never use v7 as a secret, because part of it is a timestamp.