What is the difference between UUID v4 and UUID v7?

UUID v4 is completely random — 122 random bits. UUID v7 encodes a Unix millisecond timestamp in the first 48 bits, making it sortable by creation time. v7 is better for database primary keys because it avoids random B-tree insertions.

Is UUID the same as GUID?

Yes. UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) are the same 128-bit format. UUID is the RFC 4122 standard term; GUID is Microsoft's term used in .NET, SQL Server, and Windows APIs.

Can two UUIDs ever be the same?

In theory yes, but the probability is astronomically small. For UUID v4, the chance of a collision between any two UUIDs is about 1 in 5.3 × 10^36. Generating 1 billion UUIDs per second for 85 years would give a 50% chance of just one collision.

UUID Generator

Generate cryptographically random UUID v4s or time-ordered UUID v7s in bulk. Everything runs in your browser — nothing is sent to a server.

Version

Count

Format

10 UUIDs — v4

What Is a UUID?

A UUID (Universally Unique Identifier), also known as a GUID (Globally Unique Identifier), is a 128-bit label used to uniquely identify information in computer systems. It is formatted as 32 hexadecimal characters separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx.

UUID v4 — Random

UUID v4 is randomly generated using a cryptographically secure random number generator. The probability of a collision is astronomically low (about 1 in 5.3 × 10³⁶ for a single pair). It is the most commonly used UUID version.

UUID v7 — Time-ordered

UUID v7 (RFC 9562) encodes a Unix timestamp in the most significant bits, making generated UUIDs sortable by creation time. This has significant database performance benefits — new rows have keys that are always greater than previous ones, avoiding random B-tree insertions that cause page splits and index fragmentation.

UUID vs GUID

UUID and GUID refer to the same concept. UUID is the RFC standard term (RFC 4122). GUID (Globally Unique Identifier) is Microsoft's term for the same thing, used in .NET, SQL Server, and Windows APIs. The format is identical.

When to Use UUIDs

Primary keys in distributed databases where auto-increment integers would conflict across shards
Unique identifiers for API resources (users, orders, sessions)
Idempotency keys for payment and transaction APIs
Correlation IDs for tracing requests across microservices

Related Developer Tools

Need to hash a UUID or any string? Use the Hash Generator for MD5, SHA-256 and more. Working with timestamps in your IDs? The Unix Timestamp Converter decodes the epoch embedded in UUID v7.