When would I use the nil UUID?

The nil UUID is typically used as a default or placeholder value in UUID-typed database columns or API fields, similar to NULL or zero in other types. It signals 'no UUID has been assigned yet'.

Is the nil UUID a valid UUID?

It is a valid UUID per RFC 4122, but it is reserved as a special case. Prefer a randomly generated UUID v4 for any real identifier.

Nil UUID

The nil UUID is a special UUID with all 128 bits set to zero: 00000000-0000-0000-0000-000000000000. It is defined in RFC 4122 as a sentinel value representing the absence of a real UUID.

Generated UUID

VERSION

Runs entirely in your browser

How it works

UUID v4 generation uses the browser's crypto.randomUUID() API, a cryptographically secure random number generator built into every modern browser. No JavaScript library is needed.

Processing runs in your browser

UUIDs are generated entirely in your browser. All processing happens locally in your browser tab. Our servers are not involved at any point. You can inspect this yourselfin your browser's DevTools Network tab.

Technical specification

UUID version 4 (random) is defined in RFC 4122 (IETF, 2005). A UUID v4 contains 122 random bits; the remaining 6 bits encode the version (4) and variant (10xx in bits 64–65). This tool uses the browser's crypto.randomUUID() method (W3C Web Cryptography API), which provides cryptographically strong randomness from the operating system's CSPRNG, equivalent to /dev/urandom on Linux or BCryptGenRandom on Windows.

Standard: RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace
Random bits: 122 bits (of 128 total; 6 bits encode version/variant)
Format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
Collision probability: ~50% at 2.7 × 10¹⁸ UUIDs generated

Related operations

For hashing identifiers into fixed-width values, try the hash generator. To produce strong random secrets, use the password generator. For encoding identifiers for transport, see Base64.

Frequently asked questions

When would I use the nil UUID?: The nil UUID is typically used as a default or placeholder value in UUID-typed database columns or API fields, similar to NULL or zero in other types. It signals 'no UUID has been assigned yet'.
Is the nil UUID a valid UUID?: It is a valid UUID per RFC 4122, but it is reserved as a special case. Prefer a randomly generated UUID v4 for any real identifier.