UUID Generator
Generate UUID v4 identifiers in your browser. Bulk-generate up to 1,000 at a time, lowercase or uppercase, with or without hyphens. Uses crypto.randomUUID() when available — the same secure RNG behind TLS — with a crypto.getRandomValues() fallback. 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 a 128-bit identifier where 122 bits are random. The format is 8-4-4-4-12 hex digits with the version 4 marker baked into the 13th nibble, defined by RFC 4122.
Yes. We use crypto.randomUUID() where available, falling back to crypto.getRandomValues() — the same secure RNG the browser uses for TLS. Don't use Math.random() for UUIDs; it isn't safe.
Practically, no. With 2^122 possible values you'd need to generate about 2.71 × 10^18 UUIDs to have a 50% chance of one collision. That's many lifetimes of every CPU on Earth.
UUID v4 is fully random — great for opaque IDs. ULID is lexicographically sortable (timestamp prefix) — better for DB primary keys where insertion order matters.
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).