Which version should I use?

Use v4 for general-purpose random identifiers. Use v7 or ULID for database keys, because they sort by creation time and keep indexes compact.

Can two UUIDs collide?

A version 4 UUID has 122 random bits. You would need to generate billions per second for decades before a collision became likely.

How random are the results?

They come from your browser's cryptographically secure random number generator (crypto.getRandomValues) with rejection sampling to avoid bias. Math.random() is never used.

UUID Generator and Validator - Free Online Tool

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Generate UUID v4, UUID v7 and ULID identifiers, or validate an existing UUID.