UUID v5 Generator
NewGenerate a deterministic, SHA-1-based UUID v5 from a namespace and name — the same input always produces the same UUID.
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Unlike random UUID v4, a v5 UUID is deterministic: the same namespace + name always produces the exact same UUID, computed as a SHA-1 hash of the namespace bytes concatenated with the name, per RFC 4122. This is useful for generating stable, collision-resistant IDs from existing identifiers (like a URL or email) without needing to store a lookup table.
Frequently Asked Questions
How is UUID v5 different from the more common UUID v4?
UUID v4 is purely random and different every time you generate one, even for the same "logical" thing. UUID v5 is deterministic — hashing the same namespace UUID and name string always produces the exact same UUID, which is useful when you need a stable ID derived from an existing identifier without maintaining a lookup table.
What are the predefined namespace options?
They're the four standard namespace UUIDs defined in RFC 4122 for DNS names, URLs, ISO OIDs, and X.500 distinguished names — using one of these means your UUIDs follow the same convention other RFC-4122-compliant systems use for the same kind of input.
Can I use my own namespace UUID?
Yes — select "Custom UUID" and enter any valid UUID as the namespace. This is common when an organization defines its own namespace UUID once and derives all its deterministic IDs from it.
What hashing algorithm does it use, and is it secure?
It uses SHA-1 via the browser's native Web Crypto API, exactly as RFC 4122 specifies for UUID v5. SHA-1's known cryptographic weaknesses (collision attacks) are not a practical concern here, since UUID v5 uses it purely as a good hash function for ID generation, not for any security-sensitive signature or integrity purpose.
Does anything get sent to a server?
No — the SHA-1 digest is computed entirely client-side using the browser's built-in SubtleCrypto API.