UUID v4 vs v7: choosing the right identifier

How it works

The browser crypto generator produces 128 random bits; six of them are overwritten to mark the version (4) and the variant. The result is formatted as five groups separated by hyphens: 8-4-4-4-12 hexadecimal characters.

• Version 4 UUIDs are random, not sequential. For sortable IDs look at UUID v7 or ULID.

Why it matters

Database keys, request IDs, idempotency tokens and file names all need identifiers that can be created independently. A random UUID removes the coordination and sequence leaks that auto-increment IDs bring, at the cost of not being sortable.

A worked example

crypto.randomUUID() returns something like 3f2b0c1e-9a4d-4d77-b0d2-7c9a1f5e6b8c. The 4 in the third group marks the version; the first digit of the fourth group marks the variant, which is why it is always 8, 9, a or b.

Common mistakes

• Building IDs with Math.random instead of the crypto generator.
• Expecting v4 IDs to sort chronologically.
• Storing them as case-sensitive text when the canonical form is lowercase.

Practical tips

If you need identifiers that sort by creation time, use UUID v7 or ULID instead — v7 encodes a millisecond timestamp in the leading bits. Store UUIDs in a native uuid column when the database offers one; it is smaller and faster than text.

How to use it

1. Open the tool. Everything runs in your browser tab.
2. Paste or type your input, then choose the action you need.
3. Check the result and copy it with one click.

Open the tool

Common questions