The UUID generator creates UUIDs in all versions — v1 through v7, plus NIL and MAX — and lets you generate up to 100 at once. A built-in checker validates any UUID string, returning the normalized form, version, and RFC 4122 variant.
Choosing the Right Version
v4 (random)
- Fully random, no time or hardware data embedded
- Most common choice for general identifiers
- Random values cause B-tree index fragmentation when used as database primary keys at high insert volume
v7 (recommended for database keys)
- First 48 bits are a millisecond-precision Unix timestamp
- Naturally sorted by creation time, avoids index fragmentation
- No MAC address — keeps time-ordering without leaking hardware info
v5 (deterministic)
- Same namespace + same name always produces the same UUID
- Uses SHA-1, suitable for idempotent ID generation
- Example: domain
example.comalways producescfbff0d1-9375-5685-968c-48ce8b15ae17
v1 (time + MAC)
- Embeds the generating machine's MAC address — can leak hardware identity
- Time-ordered, but the timestamp field is in the middle of the UUID, so sort order is not as clean as v7
- Avoid for new projects; use v6 or v7 instead
v3 vs. v5
Both generate deterministic UUIDs from a namespace and name. v3 uses MD5, v5 uses SHA-1. Use v5 for new projects. v3 exists only for compatibility with legacy systems that require it explicitly.
Namespace and Name for v3/v5
The default namespace is the DNS namespace UUID 6ba7b810-9dad-11d1-80b4-00c04fd430c8. A different namespace produces a different UUID for the same name, so namespaces act as isolation keys. You can supply any valid UUID as a custom namespace.
What the Checker Returns
Paste any string into the checker. It returns:
- Whether the format is valid
- Normalized lowercase form
- Version (v1–v7, or "unknown" for non-standard)
- Variant: RFC 4122 (standard), NCS (legacy), Microsoft (GUID format), or Future
- Whether it's NIL (all zeros) or MAX (all F's)
Invalid format strings get a plain "invalid" response — the checker won't guess a closest match.