How to use the UUID Generator
- Pick v4 for random identifiers or v7 for identifiers that sort by creation time.
- Enter how many you need, from 1 to 1,000, and press Generate.
- Tick uppercase, braces or no hyphens if your system expects a particular format. The list updates instantly.
- Copy the result or download it as a text file with one UUID per line.
- To check an existing ID, paste it into the inspector to see whether it is valid, which version it is and, for v1, v6 and v7, when it was created.
Features
- Version 4 from the browser’s cryptographic random generator
- Version 7 per RFC 9562, monotonic even within one millisecond
- Bulk generation of up to 1,000 UUIDs
- Uppercase, {braces} and no-hyphen output formats
- Inspector that shows version, variant and embedded timestamp
- Copy all or download as a .txt file
What a UUID is
A UUID (universally unique identifier), also called a GUID in the Microsoft world, is a 128-bit number used to label things without asking a central authority for the next free ID. It is usually written as 32 hexadecimal digits in five groups, 8-4-4-4-12, such as f47ac10b-58cc-4372-a567-0e02b2c3d479. Because anyone can create one independently with a negligible chance of a clash, UUIDs are used for database keys, file names, API request IDs, message IDs and distributed systems that merge data from many sources.
Two fields are fixed in every standard UUID. The first digit of the third group is the version (the 4 in 4372 above), and the first digit of the fourth group encodes the variant: 8, 9, a or b for UUIDs that follow the standard. The inspector in this tool reads both.
UUID versions at a glance
| Version | Built from | Typical use |
|---|---|---|
| 1 | Timestamp + MAC address | Legacy systems; reveals the machine and time |
| 3 and 5 | MD5 or SHA-1 hash of a name | The same name always gives the same UUID |
| 4 | 122 random bits | General-purpose unique IDs |
| 6 | Version 1 fields reordered | Sortable drop-in for v1 |
| 7 | Unix milliseconds + random bits | Database primary keys, event IDs |
Versions 6, 7 and 8 were added by RFC 9562, published in 2024, which replaced the original RFC 4122.
Version 4: random
A v4 UUID has 122 random bits; the other six hold the version and variant. This generator uses crypto.randomUUID(), which draws on the operating system’s cryptographically secure random source. Collisions are not a practical concern: by the birthday bound, you would need to create roughly 2.7 quintillion (2.7 × 1018) v4 UUIDs before the chance of a single duplicate reached 50%.
Version 7: sortable by time
Random keys scatter new rows across a database index, which causes page splits and poor cache use in B-tree indexes as tables grow. A v7 UUID starts with a 48-bit timestamp in milliseconds, so new IDs are always larger than older ones and land at the end of the index, much like an auto-increment number, while still being safe to create on any server. When you generate a batch here, the 12 bits after the version are used as a counter, so even UUIDs created in the same millisecond come out in strictly increasing order.
Choosing a format
- Lowercase with hyphens is the canonical form recommended by the standard; parsers must accept either case.
- Braces match the registry style used by Windows and COM, for example
{F47AC10B-58CC-4372-A567-0E02B2C3D479}. - No hyphens gives a compact 32-character string for URLs or file names. In a database, store UUIDs in a native
uuidor 16-byte binary column rather than as text.
Mistakes to avoid
Do not build UUIDs from Math.random(), which is not designed to be unpredictable or collision-resistant. Do not use a UUID as a password reset token or API secret either: a v7 UUID reveals when it was created, and identifiers often end up in logs and URLs. For secrets, use a dedicated random token from a password generator.
Frequently asked questions
What is the difference between a UUID and a GUID?
They are the same thing. GUID is the name Microsoft uses for UUIDs, and Windows tools often show them in uppercase inside braces.
Should I use UUID v4 or v7?
Use v4 when you just need a unique random ID. Use v7 for database primary keys and event logs, because v7 values sort by creation time and keep indexes compact.
Can two generated UUIDs ever be the same?
In theory yes, but the probability is so small that it is ignored in practice. A v4 UUID has 122 random bits, so duplicates are far less likely than hardware errors.
Are these UUIDs generated on a server?
No. They are created in your browser with the Web Crypto API, so they are never sent or stored anywhere.
Can I tell when a UUID was created?
Only for time-based versions. Paste a v1, v6 or v7 UUID into the inspector to see its embedded timestamp. Version 4 UUIDs contain no time information.