UUID Online Generator

About UUID

A Universally Unique Identifier (UUID) is a specific form of identifier that can be safely assumed to be unique for most practical purposes. The probability of two correctly generated UUIDs being identical is almost negligible, even if they are created by different parties in two different environments. This is why UUIDs are said to be universally unique.

In this article, we will look at the characteristics of UUIDs, how their uniqueness works, and scenarios where they can simplify resource identification. Although we will approach UUIDs from the general perspective of software interacting with database records, they are broadly applicable to any use case that requires the generation of decentralized unique IDs.

What is UUID?

A UUID is just a value that you can safely treat as unique. The risk of collision is so low that you can reasonably choose to ignore it entirely. You may see UUIDs referenced using different terminology (GUID or Globally Unique Identifier, which is Microsoft's preferred semantics), but the meaning and effect remain the same.
A true UUID is a unique identifier generated and represented by a standardized format. Valid UUIDs are defined by RFC 4122; this specification describes algorithms that can be used to generate UUIDs that remain unique between implementations without the need for a central issuing authority.

1. Version 1 – Time-Based – Combines a timestamp, a clock sequence, and a value specific to the generating device (usually its MAC address) to produce an output that is unique for that host at that point in time.
2. Version 2 – DCE Security – This version was developed as an evolution of version 1 for use in the Distributed Computing Environment ( DCE ). It is not widely used.
3. Version 3 – Name-Based (MD5) – MD5 hashes the “namespace” and “name” to create a value where the name is unique within the namespace. Generating another UUID with the same namespace and name will produce the same output, so this method provides reproducible results.
4. Version 4 – Random – Most modern systems tend to choose UUID v4 because it uses a host’s random or pseudo-random number source to issue its values. The chances of generating the same UUID twice are almost negligible.
5. Version 5 – Name-Based (SHA-1) – This is similar to version 3, but it uses the stronger SHA-1 algorithm to hash the input namespace and name. Even though the RFC refers to the algorithm as a version, this doesn't mean you should always use version 5 because it appears to be the latest. Which one you choose depends on your use case; in many cases, v4 is chosen because of its randomness. This makes it ideal for simple "give me a new identifier" scenarios.

The generation algorithm emits a 128-bit unsigned integer. However, UUIDs are more commonly seen as hexadecimal strings, which can also be stored as a 16-character binary sequence. Here is an example of a UUID string:

A496400C-1C18-1D86-DD8A-36E010D6B4FF