What is UUID v3?
UUID v3 hashes a namespace UUID together with a name (any string) using MD5, then formats the digest as a UUID. Given the same namespace and name, every system in the world derives the identical UUID — no coordination needed.
v3 or v5?
Both are name-based; v5 uses SHA-1 instead of MD5. RFC 9562 recommends v5 unless you need v3 for compatibility with an existing system. Neither is meant for security — the hash only provides deterministic uniqueness, not secrecy.
Standard namespaces
Four well-known namespace UUIDs are predefined: DNS (for domain names), URL, OID, and X.500. You can also supply any UUID of your own as a custom namespace to create your own deterministic ID space.
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