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UUID Generator

Generate random v4 UUIDs in your browser, one or many at a time.

Runs in your browser — files never leave your device

How it works

Choose how many UUIDs you need (1 to 100), click Generate, and a fresh batch appears ready to copy — Copy all grabs the whole list, one per line. Generation calls the browser’s built-in crypto.randomUUID(), which produces RFC 4122 version 4 UUIDs from a cryptographically secure random number generator — not Math.random().

A v4 UUID is 36 characters — 32 hexadecimal digits and 4 hyphens in an 8-4-4-4-12 pattern, like aba2af6e-e0ae-4000-ab7b-441a89bf0cae. Two small parts are fixed: the third group always starts with 4 (the version) and the fourth group starts with 8, 9, a or b (the variant). The remaining 122 of the 128 bits are random, and output uses the canonical lowercase form.

Uniqueness comes from scale rather than coordination. There are 2¹²² — about 5.3 × 10³⁶ — possible v4 UUIDs, and by the birthday bound you would need to generate roughly 2.71 × 10¹⁸ of them, a billion every second for about 86 years, before reaching a 50% chance of even one collision. That is why independent machines can mint IDs concurrently, with no central registry, and safely treat them as unique.

That property is exactly what distributed systems want: database primary keys that a client can create before the row is inserted, correlation and request IDs that tie one operation together across log files and microservices, idempotency keys for payment APIs, and collision-proof names for uploaded files.

Two caveats. v4 UUIDs are random, therefore unordered — used as a clustered primary key they scatter inserts across the index instead of appending, which is the niche the time-ordered UUIDv7 was created for (this tool generates v4, the general-purpose default). And although the randomness is cryptographic quality, UUIDs are identifiers, not credentials — use a dedicated token generator for secrets. Everything runs on your device, and every click of Generate produces a fresh, unrelated batch.

Frequently asked questions

Which UUID version does this generate?
Version 4 (random), as defined by RFC 4122, using the browser’s built-in crypto.randomUUID(). Apart from six fixed version-and-variant bits, all 122 remaining bits come from a cryptographically secure random number generator.
What is the difference between v4 and v1?
v1 UUIDs embed a timestamp and, historically, the machine’s MAC address — they are roughly sortable by creation time but can reveal when and where they were made. v4 is pure randomness with no embedded information, which is why it is the default for general-purpose identifiers. This tool generates v4 only.
Can two generated UUIDs collide?
In theory yes, in practice no. With 2¹²² (about 5.3 × 10³⁶) possible values, you would need roughly 2.71 × 10¹⁸ UUIDs — a billion per second for about 86 years — to reach a 50% chance of a single collision. Applications treat v4 UUIDs as unique without checking.
Is the randomness cryptographically secure?
Yes — crypto.randomUUID() draws from the Web Crypto CSPRNG, the same source as crypto.getRandomValues(), not from Math.random(). The values are unpredictable, but treat UUIDs as identifiers rather than secrets: session tokens and API keys deserve a purpose-built generator.
Why does every UUID have a 4 in the third group?
That digit is the version number, fixed by the spec, and the first character of the fourth group is always 8, 9, a or b — the variant bits. Only the other 122 bits vary. Output uses the canonical lowercase form; compare UUIDs case-insensitively and store them lowercased.
Are v4 UUIDs good database primary keys?
They are widely used for exactly that: keys can be generated on any client before insert and merged from many sources without coordination. The one cost is index locality — random values scatter inserts across a clustered B-tree instead of appending — which is the problem the newer time-ordered UUIDv7 addresses if write throughput demands it.
Are the generated UUIDs stored anywhere?
No — they are created in your browser with the Web Crypto API and exist only on this page until you leave or regenerate. Nothing is uploaded or logged, so copy what you need first; each batch is independent and cannot be recovered.

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