What is the difference between a UUID and a GUID?

UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) are virtually identical terms. UUID is the RFC 4122/9562 standard terminology, while GUID is Microsoft's historical naming convention.

What is the probability of a UUID collision?

A standard Version 4 UUID contains 122 bits of cryptographic randomness out of 128 total bits. Generating 1 billion UUIDs every second for 85 years yields an estimated collision probability of under one in a billion.

Why is UUIDv7 preferred for database primary keys?

UUIDv7 (RFC 9562) embeds a millisecond Unix timestamp in the high-order bits, providing natural time-ordered monotonic sorting. This drastically reduces database B-Tree index fragmentation compared to pure random UUIDv4.

Bulk UUID / GUID Generator

Generate cryptographically secure 128-bit unique identifiers instantly in your browser.

1 UUID(s) generated

⚡ Quick Reference Answer (AEO Summary)

A UUID (Universally Unique Identifier) is a 128-bit label formatted as 32 hexadecimal digits displayed in 5 groups separated by hyphens (8-4-4-4-12): xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx. Version 4 uses cryptographically random numbers (Web Crypto API crypto.randomUUID()), guaranteeing practically zero chance of duplicate collision across globally distributed database systems.

Quantity to Generate

Formatting Options

Include Hyphens (8-4-4-4-12) Uppercase Letters (A-F) Wrap with Braces ({...})

Generated Identifiers

🔒 Browser-native CSPRNG: Generated client-side using crypto.randomUUID() and crypto.getRandomValues(). Zero network requests made.

UUID Versions & Standards Comparison (RFC 4122 vs RFC 9562)

The IETF standard defines multiple UUID variants suited for distinct engineering use cases:

Version	Source of Entropy	Predictability	Primary Use Case
v1 (Timestamp)	60-bit timestamp + 48-bit MAC address	Predictable (leaks host MAC)	Legacy distributed systems (now deprecated).
v4 (Random)	122 bits of pseudo-random CSPRNG entropy	Completely unpredictable	Session tokens, distributed microservice request IDs, general unique keys.
v5 (Name SHA-1)	SHA-1 hash of a namespace UUID + name	Deterministic (same input gives same UUID)	Idempotent resource identification across disparate pipelines.
v7 (Epoch Time-Ordered)	48-bit Unix epoch millisecond timestamp + 74 bits random entropy	Monotonically sortable by generation time	High-write database primary keys (PostgreSQL, MySQL, CockroachDB, Spanner).

Understanding the Math Behind UUID Collision Impossibility

For standard Version 4 UUIDs, there are $2^{122} \approx 5.3 \times 10^{36}$ unique possible combinations. By applying the Birthday Paradox approximation, the number of UUIDs $n$ required to reach a 50% collision probability $p = 0.5$ is:

            n ≈ √(2 × 2122 × ln(2)) ≈ 2.71 × 1018 UUIDs
          

To put that in perspective: If an infrastructure cluster generated 1 billion UUIDs per second continuously, it would take approximately 85 years of non-stop generation to have just a 50% probability of experiencing a single collision.