UUID Generator
Generate v1 and v4 UUIDs in bulk, copy-ready.
What is a UUID?
A UUID (Universally Unique Identifier), also called a GUID (Globally Unique Identifier) in Microsoft environments, is a 128-bit identifier standardised by RFC 4122. It is represented as a string of 32 hexadecimal digits in the format xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx, where M indicates the UUID version and N indicates the variant. UUIDs can be generated independently by any system at any time with an astronomically low probability of collision — the probability of generating a duplicate UUID v4 is approximately 1 in 2^122, making collisions effectively impossible in practice.
UUID v4 is generated from random bytes and is by far the most commonly used version. It has 122 bits of randomness and provides no information about when or where it was generated. UUID v1 encodes the current timestamp and the MAC address of the generating machine, making it sortable by time of creation but revealing information about the generating system.
UUIDs are used as primary keys in databases (avoiding sequential integer IDs that can expose record counts and simplify attacks), as unique identifiers for distributed system entities, as correlation IDs for tracing requests across microservices, and as unique filenames for uploaded files.
Common mistakes
- Using sequential IDs for security-sensitive resources — Sequential integer IDs expose the total number of records and allow enumeration attacks. UUIDs for user IDs and resource URLs prevent this.
- v1 in security contexts — UUID v1 embeds your MAC address and a timestamp, potentially revealing network infrastructure details. Use v4 for security-sensitive identifiers.
- Storing as strings vs binary — Storing UUIDs as VARCHAR(36) strings is 3× less efficient than storing as BINARY(16) in databases that support it. The hyphenated string representation is for human readability only.