Version 4 UUIDs are 122 random bits plus 6 fixed bits for version and variant, so the third group always starts with 4 and the fourth with 8, 9, a or b. Make up to 1,000 at once, e.g. f47ac10b-58cc-4372-a567-0e02b2c3d479.
How to use
- Pick a version: v4 (random) or v7 (time-ordered). NIL and MAX give the special all-zero and all-F values.
- Choose how many: 1, 5, 10, 50, 100 or any number up to 1,000.
- Tap a UUID to copy it, or use Copy all and Download .txt for the whole list.
- Turn on Uppercase, No hyphens or Braces to match the format your code expects.
- Paste any UUID into Inspect to check that it is valid and see its version, variant and, for v1, v6 and v7, when it was created.
- UUIDs are created in your browser with crypto.getRandomValues, a cryptographically secure generator. Nothing is sent or stored.
- v4 has 122 random bits: the chance of a collision is negligible even across billions of IDs.
- v7 (RFC 9562) starts with a 48-bit Unix timestamp in milliseconds, so new IDs sort after old ones. That keeps database indexes compact. UUIDs generated in the same millisecond still sort in order.
- GUID is Microsoft’s name for the same 128-bit format. The braces option gives the {…} registry style.
- Your format options are remembered; generated UUIDs are not.
What a UUID is
A UUID (universally unique identifier, RFC 9562, which replaced RFC 4122 in 2024) is a 128-bit value written as 32 hex digits in five groups: 8-4-4-4-12, 36 characters with hyphens. The first digit of the third group is the version, and the first digit of the fourth group (8, 9, a or b) marks the standard variant. GUID is Microsoft’s name for the same format.
v4 or v7?
Version 4 is 122 random bits. You would need about 2.7 quintillion (2.7 × 10^18) of them for a 50% chance of a single duplicate, so collisions are not a practical concern when the generator is secure. This tool uses crypto.getRandomValues.
Version 7 starts with a 48-bit Unix timestamp in milliseconds followed by random bits. New IDs sort after older ones, which keeps B-tree indexes compact and inserts fast, so v7 is a good default for database primary keys. The trade-off: anyone holding a v7 UUID can read its creation time.
Formats and special values
Most systems expect lowercase with hyphens. Some APIs and file names want no hyphens (32 characters); .NET and the Windows registry show GUIDs uppercase in braces. The NIL UUID is all zeros and the MAX UUID all f, both defined in RFC 9562 as placeholders. UUIDs are identifiers, not secrets: don’t use them as passwords or session tokens.
Frequently asked questions
Are UUIDs really unique?
In practice, yes. A v4 UUID has 122 random bits, so even generating a billion per second for 85 years gives only about a 50% chance of one duplicate. Uniqueness depends on a good random source, which this tool takes from your browser’s secure generator.
What is the difference between a UUID and a GUID?
None in format. GUID is Microsoft’s term for the same 128-bit identifier. Windows tools often show GUIDs in uppercase inside braces, which the Braces and Uppercase options reproduce.
Should I use UUID v4 or v7 as a primary key?
v7 is usually better for database keys because values are ordered by creation time, so new rows go to the end of the index. Use v4 when you don’t want the creation time to be visible.
How do I tell which version a UUID is?
Look at the 13th hex digit, the first one of the third group: in 3f2b8c1e-9d4a-4b7e-… it is 4, so it is a v4 UUID. Paste a UUID into Inspect to see the version, variant and any embedded time.
How many UUIDs can I generate at once?
Up to 1,000 per batch. Copy all of them or download them as a .txt file with one UUID per line.
Is a UUID safe to use as a secret token?
Not as a rule. A v4 UUID from a secure generator is hard to guess, but UUIDs are designed as identifiers and often appear in logs and URLs. Use a dedicated random token for secrets.