UUID Generator — v4 & v7 Online

A UUID (Universally Unique Identifier) is a 128-bit value standardized by RFC 4122 and RFC 9562, used to uniquely identify resources across distributed systems without a central authority. The standard representation is 32 hexadecimal digits displayed in five groups separated by dashes (8-4-4-4-12), for example 550e8400-e29b-41d4-a716-446655440000. UUIDs are widely used as database primary keys, API resource identifiers, session tokens, and correlation IDs in microservice architectures.

UUID v4 generates identifiers using 122 cryptographically random bits, making each value essentially unpredictable and statistically unique. UUID v7, introduced in RFC 9562 (2024), encodes a Unix millisecond timestamp in the first 48 bits, followed by random data. This means v7 UUIDs are naturally sortable by creation time — a major advantage for database indexing, since sequential IDs reduce B-tree page splits and improve write performance. Use v4 when you need pure randomness with no embedded information, and v7 when time-ordered identifiers benefit your architecture.

For all practical purposes, yes. UUID v4 draws from a space of 2¹²² possible values (approximately 5.3 × 10³⁶). To have a 50% chance of a single collision, you would need to generate around 2.7 × 10¹⁸ UUIDs — that's 2.7 quintillion. At a rate of one billion UUIDs per second, it would take over 85 years to reach that threshold. UUID v7 further reduces collision risk by incorporating a millisecond timestamp, ensuring that IDs generated at different times are inherently different. In practice, UUID collisions are far less likely than hardware failures.

Yes, GUID (Globally Unique Identifier) is the term Microsoft adopted for the same concept. GUIDs and UUIDs follow identical formats and generation algorithms as defined in RFC 4122. The only historical difference is that some Microsoft tools display GUIDs with curly braces (e.g., {550e8400-e29b-41d4-a716-446655440000}), but the underlying 128-bit value is exactly the same. The terms UUID and GUID are fully interchangeable in modern software development.

Choose UUID v7 when your use case benefits from time-ordered identifiers. The most common scenario is database primary keys: sequential IDs dramatically improve INSERT performance on B-tree indexes (used by PostgreSQL, MySQL, and most relational databases) because new rows are always appended at the end rather than inserted at random positions. V7 is also useful for event sourcing, logging, and any system where you want to sort records by creation time without an additional timestamp column. Stick with v4 when ordering is irrelevant, when you want zero information leakage about creation time, or when working with systems that expect fully random identifiers.