UUID Generator

A version 4 UUID is 128 bits, of which 122 are random and six are fixed to mark the version and variant. They are produced by crypto.randomUUID, the browser's own implementation, backed by the same cryptographic source as the password generator.

The point of a UUID is that it needs no coordination. Two machines with no connection between them can each generate identifiers all day and never collide. Generating a billion per second for a hundred years would give roughly a one-in-a-billion chance of a single duplicate — which is why they are the default for distributed systems, offline-first apps and anything that must create records before reaching a server.

The four formats are the same 128 bits written differently. Lowercase with hyphens is the canonical form from the specification. Braces are a Microsoft convention. Without hyphens is more compact for URLs and keys.

You are seeding a database and need 500 primary keys before anything is inserted. Set the count to 500, download the list, and use it.

The trade-off worth knowing before choosing UUIDs for primary keys. Version 4 UUIDs are random, so consecutive inserts land in unrelated places in the index. On a large table that causes page splits and fragmentation, and both write throughput and index size suffer measurably compared with sequential integers.

The usual answers are an auto-increment integer as the internal key with a UUID as the public identifier, or UUID version 7, which puts a timestamp in the high bits so identifiers sort roughly by creation time while staying globally unique. This tool generates version 4, which remains the right choice when the identifier must be unguessable rather than sortable.

One security note. A version 4 UUID reveals nothing — no timestamp, no machine identifier, no sequence — which is exactly why it is suitable for a public URL where an incrementing integer would let anyone enumerate your records. That is not true of version 1, which embeds a timestamp and the network card's MAC address.