What is the difference between v4 and v7?

UUID v4 is 122 bits of pure randomness — maximally unpredictable but unordered. UUID v7 encodes the current Unix timestamp (ms precision) in the first 48 bits, so rows inserted into a B-tree index remain sequential and avoid page splits, improving database write performance.

Are the generated UUIDs truly unique?

In practice, yes. UUID v4 has 122 random bits — the probability of a collision among one billion UUIDs is roughly one in a billion billion. UUID v7 has 74 random bits but still offers collision-safety for all practical applications.

What is the "variant" field?

The variant field (2–3 bits starting at bit 64) identifies the UUID layout standard. RFC 4122 / RFC 9562 UUIDs use the "10" bit pattern, which most UUIDs you encounter will show as "RFC 4122".

Is this implementation standards-compliant?

Yes. v4 uses crypto.randomUUID() when available (all modern browsers). The v7 implementation follows RFC 9562: 48-bit ms timestamp, 4-bit version (0111), 12-bit random_a, 2-bit variant (10), and 62-bit random_b.

UUID / GUID Generator

Generate UUID v4 (random) or v7 (time-sortable) in bulk. Copy individually or all at once.

Report

Generated UUIDs

UUID Validator / Inspector

Enter a UUID to inspect:

Pick version and format

In the toolbar choose v4 (random) or v7 (time-sortable), pick standard, uppercase, or hyphen-free output, and set 1–20 items with +/− or by typing.

Generate and copy

Click Generate for a fresh list; copy one line at a time or use Copy All (newline separated). Clear removes the list.

Validate and inspect

Paste any UUID into the inspector and click Inspect to see version, variant, and format; for v7 you also get the embedded time.

Tip: v7 embeds creation time near the start of the value so rows stay more sequential in indexes, which can reduce page splits and improve write throughput.

When should I use UUIDs?

Typical uses are primary keys before insert, idempotency keys for API calls, and correlation IDs across services and logs.

Should I pick v4 or v7?

Choose v4 when you want strong randomness with no time ordering. Choose v7 when you want values to sort roughly by creation time and be gentler on database indexes.

Can generated values collide?

In practice, collisions are extraordinarily unlikely for both versions in normal workloads.

What does “variant” mean in the inspector?

It tells you which UUID layout rules apply. Most modern generators follow the RFC 4122 style variant shown in the results.

Are values sent to your servers? Are they standards-based?

No network upload—everything runs locally in your browser. v4 uses the browser’s secure random source when available; v7 follows the current time-ordered UUID specification.

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