UUID v5 Generator (RFC 4122, Name-Based)

Understanding UUID v5

A UUID v5 generator creates stable, repeatable identifiers from names. If you want the same input to always map to the same ID, UUID v5 is a great fit. It is commonly used for IDs derived from URLs, domain names, user names, or other strings where you want consistency across systems. Unlike random UUIDs, the output is deterministic, so you can regenerate the same ID whenever you need it.

UUIDs are 128‑bit values written as 36‑character strings with hyphens. Version 5 is name‑based, meaning it combines a namespace (a category) with a name (the specific value). That pairing ensures you can reuse the same name in different namespaces without collisions. For example, “example.com” in the DNS namespace is different from “example.com” in a custom namespace you define for internal projects.

How UUID v5 works

The generator takes the namespace UUID and the name, encodes the name in UTF‑8, and hashes the combined bytes with SHA‑1. It then uses the first 16 bytes of that hash to form the UUID, setting the version and variant bits required by RFC 4122. The resulting pattern looks like xxxxxxxx-xxxx-5xxx-yxxx-xxxxxxxxxxxx. The “5” indicates version 5, while the rest of the digits come from the hash.

How to use this generator

1. Select a namespace (DNS, URL, OID, X.500) or provide a custom namespace UUID.
2. Enter the name you want to convert, such as a domain, URL, or username.
3. Click Generate to create your UUID v5 value.
4. Copy the result and reuse it anywhere you need a stable identifier.

UUID v5 is useful for data migrations, syncing records between databases, and generating consistent IDs for APIs without storing a lookup table. It is also handy for software projects where you want predictable identifiers for configuration keys, feature flags, or resource names.

Namespaces

Built‑ins include 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 a custom namespace UUID to define your own identifier space.

v1 vs v5 vs v3 vs v4 (quick guide)

• v1 (time-based): Sorts by time; uses clock sequence and node.
• v5: Deterministic (SHA‑1); preferred modern choice for name‑based IDs.
• v3: Deterministic (MD5); older but interoperable; use when compatibility is required.
• v4: Random; best when you need unpredictable IDs.

Note: SHA‑1 here is used for identifiers, not cryptographic signatures.

Everything runs locally in your browser, so your input values remain private. Use this tool whenever you need consistent, human‑derived identifiers that work across applications and databases.