How to use it
- Choose v4 for random IDs or v7 for IDs that sort by creation time.
- Set how many you need (1 to 1,000) and pick the format: uppercase, with or without hyphens, with or without braces.
- Copy a single UUID with its button, copy all of them, or download them as a text file with one UUID per line.
- To inspect an existing UUID, paste it into “Check a UUID”.
How it works
A UUID (also called GUID) is a 128-bit identifier, normally written as 32 hexadecimal digits in five groups: 8-4-4-4-12. The first digit of the third group is the version, and the first digit of the fourth group encodes the variant (8, 9, a or b for standard UUIDs). The format is defined in RFC 9562, which replaced RFC 4122 in 2024.
Version 4 UUIDs are random. This tool uses crypto.randomUUID where available and otherwise crypto.getRandomValues, both of which are cryptographically secure; it never uses Math.random. With 122 random bits, the chance of two v4 UUIDs colliding is negligible: you would need to generate about 2.7 × 10^18 of them for a 50% chance of a single duplicate.
Version 7 UUIDs begin with a 48-bit Unix timestamp in milliseconds, followed by the version, a 12-bit field and 62 random bits. Because the time comes first, v7 values sort in creation order, which keeps database indexes compact and makes inserts faster than with random v4 keys. When several v7 UUIDs are created in the same millisecond, this tool uses the 12-bit field as a counter (the method described in RFC 9562, section 6.2), so a batch is always in strictly increasing order. Note that a v7 UUID reveals when it was created.
The checker accepts UUIDs with or without hyphens, in upper or lower case, in braces, or with a urn:uuid: prefix. It reports the version and variant, recognises the special nil and max UUIDs, and shows the embedded creation time for versions 1, 6 and 7.
Examples
Primary keys for a new table
Generate 100 v7 UUIDs for test data such as 0192b3c4-5d6e-7f80-9a1b-2c3d4e5f6a7b. They sort by creation time, so rows inserted later get larger keys, as with an auto-increment column.
A GUID for a Windows or .NET project
Turn on Uppercase and Curly braces to get the registry-style format {3F2504E0-4F89-41D3-9A0C-0305E82C3301} used in Visual Studio project files, COM class IDs and the Windows registry.
Checking an ID from a log
Paste 018f6e2c-1a2b-7c3d-8e4f-5a6b7c8d9e0f into the checker. It reports version 7 and the standard variant, and decodes the first 12 digits as a timestamp in May 2024, which tells you when the record was created.
Frequently asked questions
Should I use UUID v4 or v7?
Use v4 when IDs must not reveal anything, such as public tokens or file names. Use v7 for database keys and event IDs, where ordering by time improves index performance. Both have enough random bits that collisions are not a practical concern.
Are these UUIDs really unique?
They are not checked against any list, but they come from a cryptographically secure random generator, so a duplicate is so unlikely that it can be ignored for real systems. v7 values also include the current time.
Is a UUID the same as a GUID?
Yes. GUID (globally unique identifier) is Microsoft's name for the same 128-bit format. GUIDs are often shown in uppercase and in braces, which you can switch on here.
Can I use a UUID as a password or secret token?
A v4 UUID has 122 random bits, which is hard to guess, but UUIDs are designed as identifiers, not secrets, and often end up in logs and URLs. For API keys or reset links, use a dedicated random token generator.
Does the v7 timestamp use my computer's clock?
Yes. It is read from your device's clock in UTC milliseconds. If the clock is wrong, the embedded time will be wrong, but IDs in one batch are still in increasing order.
Privacy
UUIDs are generated in your browser with its cryptographic random number generator. They are not sent to a server, not stored and not logged, so nobody else sees the values you create or check.