Free UUID v4 Generator

Generate random version 4 UUIDs (RFC 4122) — one per line, up to 100 at a time. UUIDs are produced by your browser's cryptographically secure random number generator; nothing is uploaded or stored.

About this UUID Generator

A UUID (Universally Unique Identifier, also called a GUID on Microsoft platforms) is a 128-bit value written as 32 hexadecimal digits in the familiar 8-4-4-4-12 pattern, e.g. 3f2b8c1e-9d4a-4f6b-8a2e-1c5d7e9f0a3b. UUIDs let independent systems create identifiers without coordinating with each other or a central authority — two services, two devices, or two database shards can all mint IDs simultaneously with effectively zero risk of collision. This free generator produces version 4 UUIDs, the fully random variety, in batches of 1 to 100, ready to paste into code, fixtures, config files, or spreadsheets.

Generation happens entirely in your browser. The tool calls crypto.randomUUID() where available, and otherwise falls back to crypto.getRandomValues() with the version and variant bits set by hand — both draw from the operating system's cryptographically secure random source, not the predictable Math.random(). No network request is made and nothing you generate is ever seen by our servers.

How a version 4 UUID is built

A v4 UUID is 16 random bytes with 6 bits pinned to fixed values by RFC 4122:

• Version bits — the first hex digit of the third group is always 4. In byte terms, the high nibble of byte 6 is forced to 0100.
• Variant bits — the first hex digit of the fourth group is always one of 8, 9, a, or b, because the top two bits of byte 8 are forced to 10.
• The remaining 122 bits are pure randomness — about 5.3 × 10³⁶ possible values.

Thanks to the birthday paradox math, you would need to generate around 2.7 quintillion v4 UUIDs before the odds of even one duplicate reach 50%. Generating a billion UUIDs per second, that would take roughly 86 years — which is why v4 collisions are treated as a theoretical curiosity rather than an engineering concern.

UUID versions at a glance

• v1 — timestamp + node identifier. Sortable by creation time, but historically leaked the machine's MAC address, so it fell out of favor.
• v3 / v5 — deterministic, derived by hashing a namespace and a name (MD5 for v3, SHA-1 for v5). The same input always yields the same UUID.
• v4 — fully random. The default choice for most applications, and what this tool generates.
• v7 — the newer time-ordered format (RFC 9562): a Unix millisecond timestamp followed by random bits. Increasingly popular for database primary keys because inserts stay roughly sequential.

Common uses for random UUIDs

• Database primary keys — IDs can be created in the application layer before insert, merge cleanly across shards and replicas, and never reveal row counts the way auto-increment integers do.
• API resource identifiers — unguessable IDs in URLs prevent trivial enumeration of other users' resources (though they are not a substitute for real authorization checks).
• Idempotency and correlation keys — attach a UUID to a request or message so retries can be deduplicated and logs across services can be stitched together.
• Test fixtures — seed data, mock objects, and integration tests that need realistic unique IDs.
• File and object names — collision-free names for uploads in blob storage.

One trade-off worth knowing: because v4 UUIDs are random, inserting them at very high rates into a clustered index (like MySQL's InnoDB primary key) scatters writes across the index and can hurt performance compared with sequential keys. If that is your workload, consider UUIDv7 or a separate auto-increment clustering key — the trade-offs are covered in the articles linked below.

FAQ: UUID Generator