UUID Namespace Generator

Namespace UUIDs (v3 and v5) are deterministic — the same namespace + name always produces the same UUID. This is useful when you want a stable identifier derived from a meaningful name, such as generating a UUID for a URL, a user email, or a domain name. Unlike random v4 UUIDs, namespace UUIDs can be reproduced without storing them in a database.

Both v3 and v5 are name-based UUIDs. v3 uses MD5 hashing, while v5 uses SHA-1. For new projects, always prefer v5 (SHA-1) over v3 (MD5) because SHA-1 is more collision-resistant. v3 exists mainly for backward compatibility with older systems that were built before v5 was specified.

RFC 4122 defines four standard namespaces: DNS (6ba7b810-9dad-11d1-80b4-00c04fd430c8) for domain names, URL (6ba7b811-9dad-11d1-80b4-00c04fd430c8) for URLs, OID (6ba7b812-9dad-11d1-80b4-00c04fd430c8) for ISO Object Identifiers, and X500 (6ba7b814-9dad-11d1-80b4-00c04fd430c8) for X.500 distinguished names. You can also use any valid UUID as a custom namespace.

Theoretically yes (hash collision), but in practice it is astronomically unlikely. SHA-1 produces a 160-bit hash, of which 122 bits are used in v5. A collision would require a deliberate attack using known SHA-1 weaknesses, and even then producing a specific UUID from a name-based hash is not practically feasible.

Use the DNS namespace when your names are hostnames (e.g., api.example.com), and URL namespace when your names are full URLs. Use a custom namespace when you want UUIDs scoped specifically to your application — so there's no overlap with other applications that might generate namespace UUIDs from the same name strings. Generate your custom namespace once with UUID v4 and store it as a constant in your codebase.

Yes, but with caveats. Because v5 UUIDs are deterministic, a leaked namespace + algorithm allows anyone to reverse-engineer what identifier maps to what name. For sensitive data (e.g., deriving a UUID from a user's email), consider using a private custom namespace or adding a secret salt into the name before hashing. For non-sensitive content identifiers, namespace UUIDs are perfectly safe as primary keys.