UUID v3 Generator (RFC 4122, Name-Based)

Understanding UUID v3

A UUID v3 generator creates stable, repeatable identifiers from names. Unlike UUID v4, which is random, UUID v3 is deterministic: the same input will always produce the same output. This makes it ideal when you want a consistent ID for a known value, such as a username, email address, hostname, or URL. It is a reliable way to turn human-readable strings into fixed identifiers that can be stored and shared across systems.

UUIDs are 128-bit values written as 36-character strings with hyphens. Version 3 uses a namespace and a name to produce a unique result. The namespace acts like a category, and the name is the specific value inside that category. By combining them, you can have separate identifier spaces that never collide. For example, a DNS namespace lets you generate IDs for domain names, while a URL namespace can create consistent IDs for web addresses.

How UUID v3 works

The process is straightforward. The generator takes the namespace UUID and the name text, converts the name to UTF-8 bytes, then hashes the combined bytes with MD5. The 16-byte hash is formatted as a UUID and marked with version and variant bits, resulting in the familiar pattern: xxxxxxxx-xxxx-3xxx-yxxx-xxxxxxxxxxxx. The "3" indicates version 3. The rest of the bits come from the hash, which is why the output is stable for the same input.

How to use this generator

1. Select a namespace (DNS, URL, OID, or X.500) or enter a custom namespace UUID.
2. Type the name value you want to convert, such as a domain name or user ID.
3. Click Generate to create the UUID v3 value.
4. Copy the result and reuse it anywhere you need a consistent identifier.

This is useful for data migration, matching records across databases, and generating stable IDs for APIs. For example, if you have a list of customer emails and want each one to map to a repeatable ID, UUID v3 will always return the same value for the same email and namespace. That can simplify syncing between systems without storing a lookup table.

Namespaces

Common built-ins are DNS (6ba7b810-9dad-11d1-80b4-00c04fd430c8), URL (6ba7b811-9dad-11d1-80b4-00c04fd430c8), OID (6ba7b812-9dad-11d1-80b4-00c04fd430c8), and X.500 DN (6ba7b814-9dad-11d1-80b4-00c04fd430c8). You can also supply any custom namespace UUID to define your own identifier space.

When to use v1 vs v3 vs v5 vs v4

• v1 (time-based): Sorts by time; uses clock sequence and node.
• v3: Deterministic, MD5-based; best when the same input must always map to the same ID.
• v5: Like v3 but uses SHA-1; often preferred when you want a stronger hash.
• v4: Random; best for unpredictable IDs and general-purpose uniqueness.

Note: MD5 is not suitable for cryptographic signatures, but it is specified for UUID v3 and is fine for stable identifiers.

Everything runs locally in your browser, so your input strings are not uploaded or stored. Use this generator as a simple way to create repeatable IDs for names, URLs, and other structured data without needing a server-side tool.