UUID v4 Generator
Generate random UUID v4 identifiers in your browser. RFC 4122 §4.4 compliant — 122 bits of entropy, version 4 marker, variant 10x. Bulk-generate up to 1,000 at a time, lowercase or uppercase, with or without hyphens. Powered by the Web Crypto API. Nothing leaves your machine.
Anatomy of a UUID v4
128 bits split into five hex groups. The 13th hex digit is fixed at 4 (version), and the 17th is one of 8, 9, a, b (variant).
f47ac10b-58cc-4372-a567-0e02b2c3d479
└──────┘ └──┘ └┬─┘ └┬─┘ └──────────┘
8 4 4 4 12
↑ ↑
version variant122 random bits → 2^122 space Collision: ~1 in a billion after 2.7×10^17 Generated by crypto.randomUUID() RFC 4122 §4.4 compliant
What you'll use this for
UUIDs are the universal "give me a unique identifier" tool — no central coordination required.
Primary keys
Use as DB primary keys instead of auto-increment integers — no leakage of row counts.
Distributed IDs
Generate IDs on the client or any service without coordination. No race conditions.
Test fixtures
Seed test data with deterministic-looking but unique identifiers.
Idempotency keys
API clients use UUIDs as idempotency keys to safely retry POST requests.
How to generate UUIDs
Set how many
Pick a count from 1 to 1,000. The default of 10 is a good sample for clipboard work.
Pick a case
RFC 4122 specifies lowercase, but tooling often accepts either. Microsoft GUIDs are usually uppercase.
Toggle hyphens
Compact (32hex) for storage; hyphenated for human readability and most APIs.
Copy or download
One click copies all to clipboard, or save as .txt. Nothing leaves your browser.
Frequently asked questions
UUID v4 is the random variant of UUID defined in RFC 4122 §4.4. It uses 122 random bits and reserves 6 bits for the version (4) and variant (10x) markers.
Same engine, different name. This tool explicitly produces UUID v4 — useful when you want to be clear which variant you're using. See UUID Generator for the same thing under a shorter name.
Yes. Powered by the Web Crypto API (crypto.randomUUID or crypto.getRandomValues), the same RNG behind TLS. Don't use Math.random() for UUIDs — it's not safe.
Negligible. Generating 1 billion UUIDs per second for 85 years still gives you only about a 50% chance of any collision. For practical apps, treat collisions as impossible.
Yes. No signup, no limits, no ads. Generation happens entirely in your browser via the Web Crypto API.
About UUID v4
A Universally Unique Identifier (UUID), also called a GUID in Microsoft contexts, is a 128-bit number used to label resources without central coordination. RFC 4122 defines five versions; version 4 is purely random.
Format
- Canonical form:
xxxxxxxx-xxxx-4xxx-Nxxx-xxxxxxxxxxxxwhereNis8,9,a, orb. - 122 of the 128 bits are random; 4 bits encode the version (
4) and 2 bits encode the variant (10). - String length is 36 (with hyphens) or 32 (compact).
When to pick UUID v4 vs alternatives
- UUID v4 — opaque random identifiers; ideal when sortability doesn't matter.
- ULID — same length but lexicographically sortable (timestamp prefix).
- Nano ID — shorter, URL-safe, configurable alphabet.
- UUID v7 — newer time-ordered UUID variant (RFC 9562).