UUID Generator

How to use the UUID generator

1. Choose a version. v4 is fully random and the usual default. v7 begins with the current time, so the IDs sort in the order they were made.
2. Choose how many you need (1 to 100) and the format: standard lowercase, uppercase, without hyphens, or wrapped in braces as some Windows tools expect.
3. Press Generate for a fresh batch and Copy all to take them away, one per line.

The checker at the bottom reads any UUID you paste and tells you its version and variant, or why it is not valid.

What a UUID is

A UUID (universally unique identifier), also called a GUID on Microsoft platforms, is a 128-bit number written as 32 hexadecimal digits in five groups: 8-4-4-4-12. It is designed so that different computers can create identifiers at the same time, without talking to each other or a central database, and still be confident that no two will ever match.

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx M = version (1 to 8) N = variant (8, 9, a or b for the standard)

The M digit says how the UUID was made, and the first digit of the fourth group (N) says which layout family it belongs to. Every UUID this tool creates uses the standard variant defined in RFC 9562 (which replaced RFC 4122 in 2024), so the fourth group always starts with 8, 9, a or b.

Version 4 and version 7

Version 4 is a good default when you only need uniqueness. Version 7 is better for database keys: because new IDs are always larger than old ones, they are added at the end of an index instead of being scattered through it, which keeps inserts fast and the index compact. The cost is that a v7 ID tells anyone who sees it roughly when it was created, so avoid it where that would leak information.

How likely is a collision?

A v4 UUID has 122 random bits, which is about 5.3 × 10³⁶ possible values. By the birthday-paradox formula, you would need to generate roughly 2.7 × 10¹⁸ UUIDs before there is a 50% chance that any two are identical. At a rate of a billion UUIDs per second, that would take about 86 years of continuous generation. For ordinary applications, the chance of a collision is far lower than the chance of a hardware fault.

That assumes the random numbers are good. This tool uses the browser's cryptographic random generator (crypto.getRandomValues), which is designed for exactly this purpose. A UUID built from Math.random() would be much weaker and could repeat.

Worked example: reading a v7 UUID

Take 018f2b4e-7c3a-7b1c-9d2e-4a5f6c7d8e9f. The first 12 hex digits, 018f2b4e7c3a, are a 48-bit millisecond Unix timestamp: 0x018f2b4e7c3a = 1,714,418,515,002 milliseconds after 1 January 1970, which is 29 April 2024 at 19:21 UTC. The next digit, 7, is the version. The digit 9 at the start of the fourth group shows the standard variant (binary 10xx). The remaining bits are a counter and random data. Paste it into the checker above to see the same breakdown, including the creation time.

UUIDs compared with auto-increment numbers

Neither is better in every case. Sequential numbers are smaller, easier to read aloud and ideal for a single database. UUIDs make sense when data is created in several places, such as mobile apps that work offline, or when you do not want users to be able to guess other records by changing a number in a URL.

Accuracy and limits

UUIDs are generated in your browser and are not registered anywhere, so uniqueness depends on the strength of the random numbers rather than on a central authority. Version 7 counters increase within the same millisecond to keep IDs from one batch in order, but two different devices generating in the same millisecond are ordered only by their random bits. Do not use UUIDs as secrets or session tokens unless you are sure of their randomness and length.

Frequently asked questions