How do I tell which UUID version I have?

Look at the 13th hex character (start of the third group): `xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx`. M is the version digit (1-8). The 17th hex character (start of the fourth group) starts with the variant — 8, 9, A, or B for the standard RFC 4122/9562 variant.

v4 vs v7 — which should I use?

v4 (random) is great for cryptographic uniqueness and unguessability. v7 (Unix-epoch time + random) is much better for database primary keys because the leading bytes are time-ordered, so B-tree indexes stay clustered and inserts don't cause page splits. For new systems in 2025+, prefer v7 unless you specifically need unguessability.

What does 'variant' mean?

Variant identifies the layout standard. Variant `10x` (binary) — i.e. first hex char is 8, 9, A, or B — is the RFC 4122/9562 standard variant used by virtually all modern code. Other variants exist for backwards compatibility (Apollo NCS, Microsoft GUID) but you'll almost never see them.

Can the validator decode v3/v5 namespace UUIDs?

It identifies them as v3 (MD5) or v5 (SHA-1) namespace UUIDs but cannot reverse the hash to recover the original name + namespace UUID. To verify, recompute it from the known namespace + name and compare strings.

What about hyphen-less or braced UUIDs?

The validator accepts canonical (8-4-4-4-12), no-hyphens (32 hex chars), Microsoft braced ({...}), and URN-prefixed (urn:uuid:...) forms. Most APIs expect canonical form — convert before sending.

UUID Validator

Developer Tools· 30 tools

Free UUID validator and decoder. Paste a UUID and get the version (1 time-MAC, 3 namespace-MD5, 4 random, 5 namespace-SHA1, 6 reordered time, 7 Unix-epoch time, 8 custom), the variant byte, and — for time-based versions — the embedded timestamp. Distinguishes the canonical 8-4-4-4-12 form from braced, hyphenless, and URN-prefixed variations.

UUID

Position 13 · version digit (1-8)

Position 17 · variant — 8/9/A/B = RFC 4122/9562

Accepted forms: canonical, no hyphens, braced, urn:uuid:

✓ Valid

v7 — Unix-epoch time + random

Canonical01933b1f-3a4c-7c8a-b8c2-7e2f4d8b8e10

VariantRFC 4122 / 9562 (standard)

Input formcanonical

Timestamp2024-11-17T17:15:22.572Z

Decoded from Unix-epoch ms prefix

Frequently Asked Questions

References

RFC 9562 — UUID Formats — IETF

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Frequently Asked Questions

References and sources

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