UUID generator

A UUID (universally unique identifier), called a GUID in the Microsoft world, is a 128-bit number written as 32 hex digits in five groups: 8-4-4-4-12, for example f47ac10b-58cc-4372-a567-0e02b2c3d479.

UUIDs let you create IDs anywhere, on a server, in a browser or on a phone, without asking a central database for the next number, and without realistic risk of two being the same. They are used as primary keys, request and trace IDs, file names, and idempotency keys for payment APIs.

The UUIDs here are generated with your browser's cryptographically secure random number generator (crypto.getRandomValues), and nothing is sent to a server.

	UUID v4	UUID v7
Content	122 random bits	48-bit Unix timestamp in milliseconds + 74 random bits
Sort order	Random	Roughly by creation time
Reveals creation time	No	Yes, to the millisecond
Best for	General IDs, tokens, anything public	Database primary keys, logs, event streams

Both are defined in RFC 9562 (2024), which replaced RFC 4122. The version digit is the first character of the third group: 4xxx or 7xxx.

Why v7 for databases? B-tree indexes, used by PostgreSQL, MySQL and most other databases, work best when new keys arrive in order. Random v4 keys land all over the index, which causes page splits and slower inserts on large tables. Time-ordered v7 keys append near the end, much like an auto-increment column.

Take 0190a1b2-c3d4-7e5f-8a9b-0c1d2e3f4a5b as an example:

• The first character of the third group is the version: 7 here, so this is a v7 UUID.
• The first character of the fourth group shows the variant. 8, 9, a or b means the standard RFC 9562 layout used by practically all modern UUIDs.
• In a v7 UUID, the first 12 hex digits (0190a1b2c3d4) are the creation time in milliseconds since January 1, 1970, UTC. You can turn them into a date with the Unix timestamp converter after converting from hex.

The nil UUID, 00000000-0000-0000-0000-000000000000, is a special value that means "no ID". Some code uses it as a placeholder, so never hand it out as a real identifier.

• Uppercase: some systems, notably older Microsoft tools, display GUIDs in capitals. UUIDs are case-insensitive, so both forms are the same value.
• No hyphens: 32 plain hex characters, common in URLs and file names.
• Wrap in braces {…}: the registry-style GUID format used in Windows and .NET.
• Quoted, comma-separated: ready to paste into an array, an SQL IN (…) list or a test fixture.

You can generate up to 10,000 UUIDs at once and download them as a text file.

A v4 UUID has 2^122 possible values, about 5.3 × 10^36. You would need to generate roughly 2.7 × 10^18 of them before the chance of a single duplicate reached 50%. In practice, a collision is far less likely than a hardware error.

Uniqueness depends on good randomness, which is why this tool uses the browser's secure generator rather than Math.random(). A v4 UUID is unpredictable enough for IDs, but if you need a secret, such as an API key or a password reset token, use a dedicated random string with enough length and character variety.