# Uuid

Discover how the SDK represents universally unique identifiers.

An RFC 4122 universally unique identifier that the SDK uses to represent the visitor's [client ID](/reference/sdk/php/api/storage/identity-store/get-client-id).

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Use the summary below to quickly jump to a specific topic:

- [random](/reference/sdk/php/api/storage/uuid/random): Learn how to generate a random UUID.
- [parse](/reference/sdk/php/api/storage/uuid/parse): Learn how to parse a UUID from a string.
- [isValid](/reference/sdk/php/api/storage/uuid/is-valid): Learn how to check whether a string is a valid UUID.
- [equals](/reference/sdk/php/api/storage/uuid/equals): Learn how to compare two UUIDs.
- [toString](/reference/sdk/php/api/storage/uuid/to-string): Learn how to get the string representation of a UUID.