A UUID is a unique identifier used by software, databases and applications to label records, devices, users, files and other types of data.
UUIDs are designed to be extremely unlikely to repeat, which makes them useful when systems need unique values without relying on a central numbering system.
In this guide, you’ll learn what a UUID is, how UUIDs are used, how to generate one, and what to know about the different UUID versions.
By ToolNestPro | Updated September 2026
What Is a UUID?
UUID stands for Universally Unique Identifier.
It is a 128-bit value usually displayed as a group of letters and numbers separated by hyphens.
For example:
550e8400-e29b-41d4-a716-446655440000
UUIDs are commonly used when a system needs to create identifiers that are extremely unlikely to be duplicated.
They are often used for:
database records
user accounts
files and documents
devices
API requests
software objects
How to Generate a UUID
A UUID is normally generated automatically by software, a programming language or a UUID generator.
For example, a generated UUID might look like this:
7f3a2c10-9b54-4d8f-a6e2-1c7b5f9d3e40
You do not need to choose the letters and numbers yourself.
A UUID generator creates the identifier for you and helps ensure that the value is unique enough for practical use.
UUIDs are often generated when:
creating a new database record
assigning an ID to a user or object
creating API request identifiers
storing files or resources
generating unique references inside an application
How to Generate a UUID: A Simple Step-by-Step Guide
There are several UUID versions, and they are created in different ways.
The most common include:
UUID Version 1 — based partly on time and device information
UUID Version 3 — generated from a name using MD5 hashing
UUID Version 4 — generated using random values
UUID Version 5 — generated from a name using SHA-1 hashing
For general use, UUID Version 4 is one of the most commonly used because it is random and simple to generate.
Different systems may choose different UUID versions depending on how the identifier will be used.
Common UUID Mistakes
UUIDs are designed to be highly unique, but mistakes can still happen when they are created, stored or copied incorrectly.
Common issues include:
manually changing part of a UUID
copying only part of the identifier
removing hyphens when a system expects them
using the wrong UUID version for a particular application
treating UUIDs as secret passwords or security tokens
storing the value in an incorrect format
For example, a UUID should normally be kept exactly as it was generated unless the system you are using specifically requires a different format.
UUIDs are useful for identification, but they should not be treated as a replacement for encryption or secure authentication.
Common UUID Versions
Generate a UUID Online
Need a unique identifier for a database record, API request, file or software project?
Use our free UUID Generator to create a UUID instantly online.
Frequently Asked Questions
What does UUID stand for?
UUID stands for Universally Unique Identifier. It is a value used to identify records, objects, files and other data.
Are UUIDs completely unique?
UUIDs are designed so that duplication is extremely unlikely, especially when they are generated correctly.
Which UUID version is commonly used?
UUID Version 4 is widely used because it generates identifiers using random values.