1–500
How to use the UUID Generator
- 1Enter how many UUIDs you need, from 1 to 500.
- 2Tick Uppercase or Remove hyphens if your system needs that format.
- 3Click Generate to create a fresh list.
- 4Click Copy all to copy every UUID in the list, one per line.
What is a UUID?
A UUID (universally unique identifier) is a 128-bit value used to identify something without needing a central authority to hand out numbers. Because UUIDs can be created independently on any machine with practically no chance of duplicates, they are widely used for database records, API resources, file names, message IDs and session identifiers.
This tool creates version 4 UUIDs, which are generated from random numbers. It uses the browser’s cryptographically secure random number generator, and the UUIDs are created on your device and never sent or stored. For random numbers in a specific range, use the random number generator.
UUID format explained
A UUID is written as 32 hexadecimal digits split into five groups by hyphens in an 8-4-4-4-12 pattern, for example 3f2b8c1e-7a4d-4e9b-a6c2-5d8f1e0b9a47. The first digit of the third group shows the version, so a version 4 UUID always has a 4 in that position. The first digit of the fourth group shows the variant, and for standard UUIDs it is always 8, 9, a or b.
Those fixed bits use 6 of the 128 bits, leaving 122 random bits. Removing hyphens produces a compact 32-character form, and uppercase or lowercase letters represent the same value, although lowercase is the canonical form in the standard.
How unique are version 4 UUIDs?
With 122 random bits there are about 5.3 × 10^36 possible version 4 UUIDs. You would need to generate around 2.7 quintillion (2.7 × 10^18) of them before there was a 50% chance of a single duplicate. Put another way, generating 103 trillion UUIDs gives roughly a one-in-a-billion chance of any collision. For practical purposes, properly generated random UUIDs can be treated as unique.
Using UUIDs as database keys
UUIDs make good primary keys when records are created in several places, such as multiple servers, offline mobile apps or merged databases, because IDs never clash and do not reveal how many records exist. The trade-offs are size, as they take 16 bytes compared with 4 or 8 for an integer, and, for random version 4 values, poorer index locality, since new rows are inserted at random positions in the index. If you need an ID derived from content, so the same input always gives the same value, a hash generator is the better fit.
If insert performance or sort order matters, consider version 7 UUIDs, defined in RFC 9562. They begin with a timestamp so values are roughly ordered by creation time, while still including random bits for uniqueness. Many databases also offer a native UUID type that stores the value efficiently.
Frequently asked questions
What is the difference between a UUID and a GUID?
They are the same thing. GUID (globally unique identifier) is the name Microsoft uses, while UUID is the term used in the official standard. GUIDs are often shown in uppercase or wrapped in curly braces, but the underlying 128-bit format is identical.
Can two UUIDs ever be the same?
In theory yes, but with 122 random bits the probability is so small it can be ignored for real-world systems. Duplicates in practice almost always come from a faulty random number generator, which is why this tool uses the browser’s cryptographic generator.
Is a version 4 UUID safe to use as a secret token?
A version 4 UUID from a secure generator is hard to guess, but UUIDs are designed as identifiers, not secrets. For password reset links, API keys or session secrets, use a dedicated token with more randomness generated for that purpose, such as a long random string from the password generator.
Should UUIDs be uppercase or lowercase?
Either works, as comparisons should be case-insensitive. The standard recommends lowercase output, but some systems, particularly in the Microsoft ecosystem, display them in uppercase. Use the Uppercase option if your system expects it.
Are the generated UUIDs stored anywhere?
No. UUIDs are generated in your browser and are not uploaded, logged or saved. Generate a new list at any time by clicking Generate again. If you are adding them to test data, the JSON formatter can tidy the result.