UUIDv5 / v3 Namespace Generator

Given the same namespace UUID and the same name, UUIDv5 (SHA-1) and UUIDv3 (MD5) always produce the same output UUID. Use them when you need to generate a stable identifier from something that isn’t already an ID — a URL, a DNS name, an internal path, an email — and you want two systems to agree on that ID without coordinating. Prefer v5 for new work; v3 exists mainly for compatibility with older systems.

Single

Version

Namespace UUID

DNS URL OID X.500 nil

Name

Batch

One name per line. Blank lines are skipped. Namespace and version are taken from the single-mode inputs above.

Algorithm

Serialise the namespace UUID as 16 raw bytes (big-endian across all fields).
Encode the name as UTF-8 bytes.
Hash namespace_bytes + name_bytes with SHA-1 (v5) or MD5 (v3).
Take the first 16 bytes of the digest.
Overwrite the version nibble: byte[6] & 0x0f | 0x50 (v5) or | 0x30 (v3).
Overwrite the variant bits: byte[8] & 0x3f | 0x80 — the RFC 9562 variant (10xx).
Format as 8-4-4-4-12 hex.

Once a namespace is chosen for a system, don’t change it. Every downstream ID depends on the input pair; a different namespace UUID produces a completely different output for the same name.

Known reference vectors

These are checked against RFC 4122 Appendix B and independent implementations. Type www.example.org or python.org in the single form above with the DNS namespace to reproduce.

Version	Namespace	Name	Expected UUID
v5	DNS	www.example.org	74738ff5-5367-5958-9aee-98fffdcd1876
v5	DNS	python.org	886313e1-3b8a-5372-9b90-0c9aee199e5d
v3	DNS	www.example.org	0012416f-9eec-3ed4-a8b0-3bceecde1cd9
v3	DNS	python.org	6fa459ea-ee8a-3ca4-894e-db77e160355e