UUID Generator

A UUID (Universally Unique Identifier) is a 128-bit identifier designed to be unique across space and time without requiring a central authority. The 32 hexadecimal characters (plus four hyphens) encode 128 bits, giving UUID v4 approximately 5.3 × 10³⁶ possible values — making collisions statistically negligible in real-world use. Standardized in RFC 9562 (formerly RFC 4122), UUIDs are widely used as database primary keys, API request IDs, session tokens, and any other context where a unique identifier is needed. Each client can generate IDs independently without coordination.

UUID Versions: Differences and When to Use Each

v4 is generated from cryptographically secure random bytes, making it the most general-purpose version — use v4 when you have no special requirements. v1 embeds a timestamp (100-nanosecond intervals since October 15, 1582) and a node identifier (this tool uses random bytes for privacy). The embedded timestamp makes v1 generation order traceable, which can be a privacy concern. v7 is newly standardized in RFC 9562 and places a Unix millisecond timestamp in the high bits, so UUIDs sort lexicographically in time order. This makes v7 highly efficient for database indexes in PostgreSQL, MySQL, and other systems, and it is increasingly adopted in modern applications.

Common Use Cases

Database table primary keys (v7 is especially advantageous for sorted indexes in PostgreSQL and MySQL), request tracing IDs across microservices such as X-Request-ID headers, unique entity identifiers in distributed systems where a central ID server is impractical, bulk generation of test or seed data, and unique file naming for uploaded assets. The 'no hyphens' format is handy for embedding in URLs or filenames, while the 'braces' format matches the UUID notation convention used in C# (.NET) and some Windows APIs. Bulk-generating UUIDs and downloading them as a text file is useful for pre-populating a database table or seeding a development environment efficiently.