UUID v4 Generator — Free Online Random UUID Creator

A UUID v4 is a random 128-bit identifier that is virtually guaranteed to be unique. Generate one instantly, no signup required. Uses your browser's cryptographic random number generator for true randomness.

Generate a UUID v4

1. Open the UUID Generator
2. Click Generate 1 for a single UUID or Generate 10 for a batch
3. Click Copy to copy to clipboard

What a UUID v4 Looks Like

550e8400-e29b-41d4-a716-446655440000

Five groups of hex characters: 8-4-4-4-12 (36 characters with hyphens, 32 without).

Position	Meaning
xxxxxxxx	Random
xxxx	Random
4xxx	Version (4 = random)
yxxx	Variant (y = 8, 9, a, or b)
xxxxxxxxxxxx	Random

The "4" in the third group tells you it is version 4. The first hex digit of the fourth group (8, 9, a, or b) indicates the UUID variant.

Why UUID v4 Is the Default Choice

There are 5 UUID versions. v4 is the most widely used because:

• No dependencies: Does not need a MAC address (v1), namespace (v3/v5), or monotonic counter (v7)
• Simple: Just random bytes in a specific format
• Private: Reveals no information about the generator (unlike v1 which leaks your MAC address and timestamp)
• Sufficient for most use cases: Database primary keys, session tokens, correlation IDs, file names

When to Use UUID v4

• Database primary keys: Use v4 when you need unique IDs across distributed systems without coordination. No central authority needed.
• API request IDs: Attach a UUID to each API call for tracing and debugging. The JSON Formatter helps inspect API responses with these IDs.
• Session tokens: Generate unique session identifiers for user authentication.
• File naming: Avoid collisions when multiple processes create files simultaneously.
• Idempotency keys: Prevent duplicate payment processing by tagging each request with a UUID.

UUID v4 in Programming Languages

• JavaScript: crypto.randomUUID()
• Python: import uuid; str(uuid.uuid4())
• Java: UUID.randomUUID().toString()
• Go: uuid.New().String() (google/uuid package)
• Linux: uuidgen or cat /proc/sys/kernel/random/uuid

All valid. For a quick UUID during development without opening a terminal, the browser tool is fastest.

Collision Probability

UUID v4 has 122 random bits (6 bits are fixed for version and variant). The number of possible UUIDs: 2¹²² = 5.3 × 10³⁶. To have a 50% chance of collision, you need approximately 2.71 × 10¹⁸ UUIDs. That is 2.71 quintillion. If you generated 1 billion per second, it would take 85 years.

Related: Hash Generator for creating checksums, Password Generator for secure passwords, Base64 Encoder for encoding IDs in URLs.