What is a UUID?
A UUID (Universally Unique Identifier), also called a GUID (Globally Unique Identifier), is a 128-bit identifier formatted as a string of hexadecimal digits grouped by hyphens — for example: 550e8400-e29b-41d4-a716-446655440000. The “universally unique” part means that generating one gives you an ID that is, for all practical purposes, unique across the entire world — no central registry required.
UUIDs are widely used in software to identify records in databases, track sessions, name files, and connect data across different systems without risking collisions. Version 4 UUIDs (v4) are generated randomly, making them unpredictable and safe to use in public-facing contexts.
What Does This Tool Do?
This tool generates one or more version 4 UUIDs instantly. You can copy a single UUID or generate a batch. All generation happens locally in your browser using a cryptographically secure random number generator.
How to Use This Tool
- Click Generate to create a new UUID.
- Use the copy button to copy it to your clipboard.
- Generate multiple UUIDs at once if you need a batch.
Common Use Cases
- Database primary keys: Use UUIDs as unique IDs for database records to avoid sequential ID guessing.
- File naming: Give uploaded files unique names to prevent overwrites.
- Testing and mocking: Need fake but realistic IDs for test data? UUIDs are the standard choice.
- Distributed systems: Generate IDs on the client side without needing a server to assign them.
UUID Versions at a Glance
| Version | Based on | When to use |
|---|---|---|
| v1 | Timestamp + MAC address | Legacy; leaks the generating machine’s identity |
| v3 | MD5 hash of a name + namespace | Deterministic IDs from names (deprecated hash) |
| v4 | Random bits | The default choice — unpredictable, no coordination needed |
| v5 | SHA-1 hash of a name + namespace | Deterministic IDs from names |
| v7 | Timestamp + random bits | Newer standard (RFC 9562); sortable by creation time, great for database keys |
This tool generates v4 — the most widely used version. If you’re choosing a UUID type for new database primary keys and insert performance matters, v7 is worth considering because its time-ordered prefix keeps B-tree indexes compact.
Anatomy of a UUID
Take 550e8400-e29b-41d4-a716-446655440000:
- The digit in the third group’s first position (
4here) is the version. - The first character of the fourth group (
ahere) encodes the variant — for standard UUIDs it’s always8,9,a, orb. - Everything else in a v4 UUID is random: 122 bits of entropy.
That’s why you can always identify a v4 UUID by the pattern xxxxxxxx-xxxx-4xxx-[89ab]xxx-xxxxxxxxxxxx.
Frequently Asked Questions
Are UUID v4 values truly unique?
With 2¹²² possible values (about 5.3 × 10³⁶), the probability of generating the same UUID twice is astronomically small. For all practical purposes, they are unique.
Is there a difference between UUID and GUID?
The terms refer to the same concept. UUID is the standard term (from RFC 4122); GUID is Microsoft’s name for the same thing.
Is my data private?
UUIDs are generated entirely in your browser using the Web Crypto API. No data is sent to any server.
Should I use UUIDs or auto-increment integers as database keys?
UUIDs let you generate IDs anywhere (client, multiple servers) without coordination and don’t reveal how many records exist. Integers are smaller, faster to index, and human-friendly. A common middle ground: an internal integer key plus a public-facing UUID. For UUID keys at scale, prefer time-ordered v7 to avoid index fragmentation.
Are UUIDs case-sensitive?
No. RFC 9562 specifies that UUIDs are output as lowercase but must be accepted case-insensitively — 550E8400… and 550e8400… are the same UUID. Lowercase is the convention.