.. _introduction:

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

ramsey/uuid is a PHP library for generating and working with RFC 9562_ (formerly RFC 4122_) version 1, 2, 3, 4, 5, 6, 7, and 8 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 9562_ (formerly 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://www.rfc-editor.org/rfc/rfc4122 .. _RFC 9562: https://www.rfc-editor.org/rfc/rfc9562