.. _introduction: ============ Introduction ============ ramsey/uuid is a PHP library for generating and working with `RFC 4122`_ version 1, 2, 3, 4, 5, 6, and 7 universally unique identifiers (UUID). ramsey/uuid also supports optional and non-standard features, such as GUIDs and other approaches for encoding/decoding UUIDs. What Is a UUID? ############### A universally unique identifier, or UUID, is a 128-bit unsigned integer, usually represented as a hexadecimal string split into five groups with dashes. The most widely-known and used types of UUIDs are defined by `RFC 4122`_. A UUID, when encoded in hexadecimal string format, looks like: .. code-block:: text ebb5c735-0308-4e3c-9aea-8a270aebfe15 The probability of duplicating a UUID is close to zero, so they are a great choice for generating unique identifiers in distributed systems. UUIDs can also be stored in binary format, as a string of 16 bytes. .. _RFC 4122: https://tools.ietf.org/html/rfc4122