UUID version
Count
5
Generated UUIDs
Click Generate to create UUIDs
What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. The standard format is 32 hexadecimal digits in five groups: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. The probability of generating the same UUID v4 twice is astronomically small.
UUID v1 uses a timestamp and MAC address. UUID v4 uses random numbers and is most commonly used. UUID v5 uses a namespace and name with SHA-1 hashing — the same namespace and name always produce the same UUID, making it useful for deterministic ID generation.
Frequently asked questions
What is the difference between UUID versions?
v1 includes a timestamp and device MAC address — traceable but ordered. v4 is fully random — most commonly used for database keys. v5 is deterministic — the same input always produces the same UUID, useful for generating consistent IDs from names.
Can two UUIDs ever be the same?
In theory yes, but the probability is so small it is practically impossible. UUID v4 has 2^122 possible values — about 5.3 undecillion. You would need to generate 1 billion UUIDs per second for 100 years before the probability of a collision reached 50%.
What are UUIDs used for?
Database primary keys, session identifiers, API keys, file names for uploaded content, tracking identifiers, and any scenario where you need a globally unique ID without a central coordination authority.
Is UUID the same as GUID?
GUID (Globally Unique Identifier) is Microsoft's term for UUID. They are functionally identical — both refer to the same 128-bit identifier format defined in RFC 4122.
UUID versions
v1 — timestamp + MAC address
v4 — fully random (most used)
v5 — SHA-1 of namespace + name
Common uses
Database primary keys
Session identifiers
API request tracking
File upload names
Distributed system IDs
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