What Is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by the Open Software Foundation (OSF) and defined in RFC 4122. It is typically represented as a 32-character hexadecimal string divided by hyphens:
`
550e8400-e29b-41d4-a716-446655440000
`
UUIDs are designed to be unique across both space and time — meaning two UUIDs generated independently anywhere in the world should never collide.
What Is a GUID?
A GUID (Globally Unique Identifier) is Microsoft's implementation of the UUID standard. Functionally, GUIDs and UUIDs are identical — they follow the same RFC 4122 format and the same 128-bit structure. The terms are interchangeable. Microsoft coined "GUID" for use in Windows COM and .NET environments.
UUID Versions Explained
There are five official UUID versions, each with a different generation strategy:
| Version | Generation Method | Best Use Case |
|---|---|---|
| v1 | Time-based + MAC address | Ordered by time; reveals device info |
| v2 | DCE Security | Rarely used |
| v3 | MD5 hash of name + namespace | Deterministic; reproducible |
| v4 | Random | General-purpose unique IDs |
| v5 | SHA-1 hash of name + namespace | Deterministic; more secure than v3 |
UUID v4 is by far the most commonly used version in modern applications. It generates a 122-bit random number, making collisions practically impossible (odds of 1 in 5.3×10³⁶).
When Should You Use UUID v4?
UUID v4 is the right choice when:
- You need a unique identifier for database records (primary keys)
- You're generating session tokens or correlation IDs
- You want IDs that cannot be guessed sequentially (security benefit)
- You don't need time-ordering of IDs by their value
Generate UUIDs Instantly
FuaHub's UUID Generator creates cryptographically secure UUID v4 values using the browser's built-in crypto.getRandomValues() API:
1. Open the [UUID Generator](/tools/dev/uuid-generator).
2. Select the quantity you need (1 to 100).
3. Choose your format: standard, uppercase, or no hyphens.
4. Click Copy All to paste directly into your code.
All generation happens locally in your browser — no server is involved.
UUID Collision Probability
The probability of generating two identical UUID v4 values is astronomically small. To have even a 50% chance of a collision, you would need to generate approximately 2.7 quintillion (2.7 × 10¹⁸) UUIDs. For any practical application, UUID v4 uniqueness is guaranteed.