UUID Online Generator

About UUID

A Universally Unique Identifier (UUID) is a specific format identifier that, in most practical use cases, can be safely assumed to be unique. The probability of two correctly generated UUIDs being identical is so negligible that it can be safely ignored, even if they are created by different parties in different environments. This is why UUIDs are referred to as universally unique.

In this article, we will explore the characteristics of UUIDs, how their uniqueness works, and the scenarios in which they can simplify resource identification. Although we will discuss UUIDs from the general perspective of software and database interactions, they are widely applicable to any use case requiring the generation of distributed unique IDs.

What is a UUID?

A UUID is simply a value you can safely treat as unique. The risk of collision is extremely low, and you can reasonably choose to completely ignore it. You may encounter UUIDs referenced using different terminology (such as GUID, or Globally Unique Identifier, which is Microsoft's preferred term), but the meaning and effectiveness remain unchanged.
A true UUID is a unique identifier generated and represented according to a standardized format. A valid UUID is defined by RFC 4122; this specification describes the algorithms usable for generating UUIDs, which ensure uniqueness across implementations without requiring a central registration authority.

1. Version 1 - Time-based - Combines a timestamp, clock sequence, and a value specific to the generating device (usually its MAC address) to produce a unique output for that machine at that moment.
2. Version 2 - DCE Security - This version was developed as an extension of version 1 for use in distributed computing environments (DCE). It has not been widely adopted.
3. Version 3 - Name-based (MD5) - Uses MD5 hashing of a "namespace" and a "name" to create a unique value within that namespace. Generating another UUID with the same namespace and name will produce the same output, thus providing reproducible results.
4. Version 4 - Random - Most modern systems tend to prefer UUIDv4 because it uses the machine's random or pseudo-random number source to generate its value. The probability of generating two identical UUIDs is so negligible that it can be safely ignored.
5. Version 5 - Name-based (SHA-1) - Similar to version 3, but it uses the stronger SHA-1 algorithm to hash the input namespace and name. Although RFC refers to this as a version, it does not mean you should always use version 5, since it appears to be the latest version. Your choice depends on your use case; in many situations, choosing v4 is preferred due to its randomness, making it the ideal choice for simple "give me a new identifier" scenarios.

The generation algorithm produces a 128-bit unsigned integer. However, UUIDs are most commonly represented as hexadecimal strings and can also be stored as a 16-byte binary sequence. Below is an example of a UUID string:

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