UUID Generator
Generate UUID v4 identifiers locally in your browser for testing, development, mock data and unique IDs.
UUID Generator online
Generate Universally Unique Identifiers — version 4, from your browser's cryptographic random source — one at a time or in bulk, for IDs that never need a central registry.
How to use this tool
- Choose how many you need: one, ten, or a batch with the Count field.
- Optionally tick Uppercase if your system expects shouty hex.
- Click Generate and copy the list from the result panel.
Common uses
Primary keys for offline-first apps and test fixtures, idempotency and correlation IDs in API work, naming uploaded files so they can never collide, and seeding sample data in demos and load tests.
How it works
A version 4 UUID is 122 bits of randomness dressed in a fixed pattern: 32 hex digits in five groups (8-4-4-4-12), with the version nibble fixed at 4 and the variant bits fixed at 10. The randomness comes from crypto.getRandomValues — the same cryptographic source your browser uses for security work — so generated IDs are suitable for real systems, not just examples. With 122 random bits, collisions are a practical impossibility: you would need billions of billions of IDs before chance produced a duplicate.
Worked example
A generated ID such as 3f6b2a90-4c1d-4e8f-9a2b-5d7c0e1f8a34 shows the pattern: the third group starts with 4 (the version) and the fourth group starts with 8, 9, a or b (the variant). Generate a batch of 1,000 for a data import and every one is unique for any practical purpose — no database round-trip, no coordination, no sequence to leak how many records you have.
Privacy and browser processing
UUIDs are generated in your browser from its cryptographic random source — nothing is uploaded or stored.
Frequently asked questions
Why version 4 specifically?
It is the purely random variant — no timestamp or MAC address involved, so it leaks nothing about when or where it was made. Newer versions (7, with time ordering) exist, but v4 remains the universally supported default in databases and libraries.
Can two generated UUIDs ever collide?
In principle yes, in practice no: a collision needs on the order of 10^18 IDs before probability reaches even one in a billion territory for a handful of duplicates — the birthday bound for 122 bits is about 2.7 × 10^18 for a 50% chance. Systems generating millions per second still never see one.
Should I use these as database primary keys?
Widely done, with one trade-off: random keys scatter inserts across the index, which can fragment clustered indexes on very large tables. Many systems accept that cost for the merge-anywhere benefit; high-volume single-database designs sometimes prefer sequential or time-ordered IDs instead.
Uppercase or lowercase — does it matter?
The value is identical; hex case is presentation. The canonical form is lowercase, and most libraries output lowercase, but some systems (Windows GUID tooling) display uppercase. Match what your system compares against, since string comparison is case-sensitive in some tools.
Are the UUIDs generated on a server?
No — they are generated in your browser from its cryptographic random number generator. Nothing is requested, logged or stored.