UUID Generator
Generate random UUIDs instantly. Choose v4 (random), v7 (sortable timestamp), or NIL. Bulk output as plain text, JSON array, or uppercase.
UUID Generator FAQ
What is a UUID?
UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. It is formatted as 32 hexadecimal digits grouped as 8-4-4-4-12, separated by hyphens: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. UUID is also known as GUID (Globally Unique Identifier) in Microsoft ecosystems. They are used as database primary keys, session tokens, request trace IDs, and file names to avoid collisions across distributed systems.
What is the difference between UUID v4 and UUID v7?
UUID v4 is randomly generated โ all 122 non-reserved bits are random, giving a collision probability so low it is negligible for any practical use. UUID v7 uses the current Unix timestamp (in milliseconds) for the first 48 bits, followed by random bits. This makes v7 UUIDs lexicographically sortable by generation time, which is much more efficient for database indexes than v4. UUID v7 was standardized in RFC 9562 (2024) and is now preferred for database primary keys in new projects.
What is a NIL UUID?
The NIL UUID is 00000000-0000-0000-0000-000000000000 โ all 128 bits set to zero. It is defined in the UUID standard as a special sentinel value meaning 'no UUID', similar to NULL. It is useful in test data when you need a UUID-typed field that explicitly represents an absent or unset value, without using an actual random UUID that might accidentally match a real record.
Are generated UUIDs guaranteed to be unique?
UUID v4 has 122 bits of randomness. To have even a 1% chance of a single collision, you would need to generate 2.6 ร 10ยนโธ UUIDs. In practice, for any application generating millions of UUIDs, the probability of collision is astronomically small. UUID v7 has slightly fewer random bits (74 vs 122) because some bits carry the timestamp, but the combination of timestamp + random still makes collisions effectively impossible in practice.
What is GUID and how is it different from UUID?
GUID (Globally Unique Identifier) is Microsoft's implementation of UUID. Technically they are the same format โ 128-bit identifiers in the xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx format. The term GUID is used in Windows, .NET, SQL Server, and COM; the term UUID is used in Linux, macOS, databases like PostgreSQL and MySQL, and web APIs. They are interchangeable.
Can I use these UUIDs as database primary keys?
Yes โ with a version consideration. UUID v4 is random and scatters inserts across a B-tree index, causing page splits and poor write performance at scale. UUID v7 is time-sorted and inserts sequentially, making it much more efficient for large tables. For new projects using PostgreSQL 17+ or MySQL 8.4+, use UUID v7. For SQLite or smaller datasets, v4 is fine. Generated UUIDs here are never stored โ they are completely safe to use in your own systems.