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A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 9562 (formerly RFC 4122). UUIDs are designed to be unique across all systems without requiring a central registration authority. They are widely used in databases, distributed systems, APIs, and software development to identify resources, records, and entities without the risk of collision.
The standard UUID format consists of 32 hexadecimal digits displayed in five groups separated by hyphens, following the pattern 8-4-4-4-12. For example: 550e8400-e29b-41d4-a716-446655440000. This format is consistent across all UUID versions and is recognized by virtually every programming language, database, and framework.
UUIDs solve a fundamental problem in distributed computing: how to create identifiers that are guaranteed to be unique without coordination. Unlike auto-incrementing integers that require a central database, UUIDs can be generated independently on any device, at any time, and still maintain practical uniqueness. The probability of collision for random UUIDs (v4) is astronomically small — you would need to generate approximately 2.71 quintillion UUIDs to have a 50% chance of a single duplicate.
Every UUID follows the same 128-bit structure, divided into five segments. The version nibble (bits 48–51) identifies the generation algorithm, while the variant bits (bits 64–65) confirm RFC compliance.
In this diagram, V represents the version nibble (1, 4, or 7), and y represents the variant bits. The remaining x positions hold version-specific data — timestamps for v1 and v7, or cryptographically random bits for v4.
Generated from a timestamp (100-nanosecond intervals since October 15, 1582) combined with a clock sequence and node identifier. Provides natural chronological ordering and embeds creation time, but may expose system information through the node field.
Learn more →Generated entirely from cryptographically secure random numbers. The most widely used UUID version — simple, fast, and privacy-preserving. No timestamp or machine information is embedded, making collisions theoretically possible but practically impossible.
Learn more →A modern UUID format combining a Unix timestamp (millisecond precision) with random data. Designed for database-friendly sequential ordering while maintaining randomness. Ideal for primary keys in distributed databases where index locality matters.
Learn more →Choosing the right UUID version depends on your use case. Here is a quick comparison to help you decide which version fits your needs best.
| Feature | Version 1 | Version 4 | Version 7 |
|---|---|---|---|
| Generation method | Timestamp + node | Random | Timestamp + random |
| Sortable by time | Partially | No | Yes |
| Database index performance | Good | Poor (random scatter) | Excellent |
| Privacy | May expose time/node | Fully anonymous | Exposes creation time |
| Collision risk | Very low | Negligible | Negligible |
| Best for | Audit trails, legacy systems | General purpose, APIs | Database PKs, event logs |
crypto.getRandomValues). No data is sent to any server, ensuring complete privacy and instant performance.Math.random(), ensuring UUIDs suitable for security-sensitive applications.