============
Introduction
============

ramsey/uuid is a PHP library for generating and working with [RFC4122]_ version
1, 2, 3, 4, and 5 universally unique identifiers (UUID). ramsey/uuid also
supports optional and non-standard features, such as version 6 UUIDs [UUIDV6]_,
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 [RFC4122]_.

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.