UUIDs (Universally Unique Identifiers) are 128-bit numbers used to uniquely identify information in computer systems without a central authority. They are typically represented as a series of hexadecimal digits. UUIDs are essential for ensuring unique identification in distributed systems, databases, and other scenarios.
Version 1 UUIDs are based on the current timestamp and the MAC address of the machine generating them, ensuring uniqueness but raising privacy concerns. Version 3 and Version 5 UUIDs use a namespace identifier and a name, hashed with MD5 (Version 3) or SHA-1 (Version 5), making them deterministic and useful for consistent identifiers.
Version 4 UUIDs are randomly generated, making them highly unique without a predictable pattern, beneficial for applications needing high security or privacy.
Version 6 and Version 7 UUIDs address modern needs. Version 6 reorders fields of Version 1 for better database indexing. Version 7 introduces a time-ordered generation mechanism for better performance in scenarios needing sequential identifiers.
For more details, refer to the RFCs 9562.
Is a UUID v4 truly random?
Yes — UUID v4 uses 122 random bits (the remaining 6 bits are fixed to mark the version and variant), generated with a cryptographically secure random number generator in this tool, giving a collision probability low enough to treat as effectively unique.
Which UUID version should I use?
Use v4 for general-purpose random identifiers, v7 for time-ordered IDs that sort well in a database index, and v1/v6 only if you specifically need timestamp-plus-node-based generation.
Are UUIDs generated in my browser sent anywhere?
No — generation happens entirely client-side in JavaScript; nothing is transmitted to a server.