What is a UUID?
A UUID is a 128-bit identifier that is unique without a central authority. Learn UUID v4 vs v1 and generate one free.
A UUID (Universally Unique Identifier), also called a GUID, is a 128-bit value used as an identifier that is practically guaranteed to be unique without any coordination between systems. You will see them as 32 hex digits in five dash-separated groups: 8-4-4-4-12.
Why UUIDs are unique
A random UUID has 122 bits of randomness. The number of possible values is so large (about 5×10³⁶) that generating billions of them still gives a negligible chance of a collision. This lets independent services mint IDs offline without ever asking a database for the next number.
v4 vs v1
UUID v4 is fully random — the most common choice for database keys and request IDs because it leaks no information. UUID v1 encodes a timestamp and the machine’s MAC address, making it time-sortable but privacy-leaky. Newer v7 combines a timestamp prefix with randomness for sortable-yet-random keys.
When to use one
Use a UUID when you need an identifier that multiple services can create independently — distributed systems, idempotency keys, file names, or public IDs you do not want to be guessable sequential integers.
Try it now — free, no signup
Use the UUID generator in your browser. Then, when you need it at scale with an API key and higher limits, grab the full Eveses API.