The Nil UUID is a special UUID in which all 128 bits are set to zero: 00000000-0000-0000-0000-000000000000. It is defined by the UUID standard as a guaranteed non-value.
Use this page to copy the Nil UUID or to understand how it differs from a normal generated identifier.
What is the Nil UUID used for?
The Nil UUID acts as a placeholder, default, or "no value" marker — similar to how null is used elsewhere. For example, an application might use it to represent the absence of a parent record or an uninitialised identifier.
Because it is a single, well-known constant, every system recognises it as a special value rather than a real, unique identifier.
Nil UUID vs Max UUID
RFC 9562 also defines the Max UUID, which is the opposite: all bits set to one (ffffffff-ffff-ffff-ffff-ffffffffffff). Like the Nil UUID, it is reserved as a special sentinel value.
Neither the Nil nor Max UUID should be treated as a generated, unique identifier — they are intentionally fixed constants.
Frequently asked questions
- What is the Nil UUID?
- It is the special UUID with every bit set to zero: 00000000-0000-0000-0000-000000000000, used to represent a null or default value.
- Is the Nil UUID a valid UUID?
- Yes. It is explicitly defined by the UUID specification as a valid, reserved value, but it is not a unique generated identifier.
- When should I use the Nil UUID?
- Use it as a sentinel for "no value" or as a default before a real UUID is assigned, where using null is not convenient.