Identifiers that never collide, no committee required
Every system needs to name things — records, sessions, uploads, devices, events — and sequential numbering breaks the moment two machines create records simultaneously, or leaks business intelligence (order #4051 tells competitors your volume). UUIDs solve naming by brute mathematical force: 128 random bits formatted as xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx, drawn from a space so vast that collisions are a theoretical curiosity. This generator produces version-4 UUIDs from your browser's cryptographic randomness — one or five hundred at a time, uppercase or hyphen-less if your schema demands it.
How to generate UUIDs
- Set how many you need (1–500).
- Optionally toggle uppercase or remove hyphens to fit your system's format.
- Click Generate UUIDs, then copy the batch — one per line.
How unlikely is a collision, really?
A v4 UUID has 122 random bits — about 5.3×10³⁶ possible values. Generate a billion UUIDs per second for a century and the probability of a single duplicate stays around one in a billion. In engineering terms: you may treat them as unique without checking, which is the entire point — no central registry, no coordination between services, no lock on a counter. Every part of a distributed system can mint identifiers independently and merge data later without conflicts.
Anatomy of the format
The shape is 32 hex digits in 8-4-4-4-12 grouping. Two characters are fixed by the standard: the third group starts with 4 (the version — pure randomness) and the fourth group starts with 8, 9, a or b (the variant). The other 30 hex digits are cryptographically random — this tool sources them from crypto.getRandomValues(), the browser's CSPRNG, not the predictable Math.random() that toy generators use. Predictable IDs are a real vulnerability class when identifiers gate access to resources (the “guess the invoice URL” attack).
Where they slot in daily work
- Database primary keys in distributed systems — and anywhere sequential IDs would leak volumes.
- Test fixtures: a batch of 50 realistic IDs for seeding, mocking and load scripts (bulk mode exists for exactly this).
- File and asset names: uploads that can never overwrite each other.
- Correlation IDs: stamp one UUID across a request's path through microservices and grep the logs end to end.
- Format note: store lowercase-with-hyphens (the canonical form) unless a legacy schema says otherwise; the toggles here serve those legacy moments.
Need a name nobody else will ever pick, with zero meetings about it? That's the UUID job description — generate away.
Quick reference
| Property | Detail |
|---|---|
| Version | UUID v4 (random) — RFC 4122 |
| Randomness | crypto.getRandomValues (CSPRNG) |
| Entropy | 122 random bits ≈ 5.3×10³⁶ values |
| Bulk | 1–500 per batch, one per line |
| Format options | Uppercase, hyphen removal |
| Collision risk | Negligible by design — no checking needed |
| Processing | 100% in-browser |
Frequently asked questions
Can two generated UUIDs ever be the same?
Mathematically possible, practically never — 122 random bits means even a billion UUIDs per second for a century leaves duplicate odds around one in a billion. Systems worldwide treat v4 UUIDs as unique without verification.
Why does the third group always start with 4?
That digit encodes the UUID version — 4 means “generated from random bits”. The first character of the fourth group (8/9/a/b) encodes the variant. Both are required by RFC 4122; the remaining 30 hex digits are pure randomness.
Are these UUIDs secure enough for session tokens?
They're generated with cryptographic randomness, which is the right foundation. For session identifiers, frameworks' built-in token mechanisms remain best practice, but a v4 UUID from a CSPRNG is far beyond guessable.
Should I store UUIDs with or without hyphens?
Canonical form is lowercase with hyphens — maximum interoperability and readability. Strip hyphens only when a legacy column or API contract demands the 32-character form; the toggle here covers that case.