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Encoders, converters & dev utilities
Nil UUID — the All-Zero UUID (00000000-…)
The nil UUID is the special all-zero UUID defined by RFC 9562: 00000000-0000-0000-0000-000000000000. Every one of its 128 bits is zero, so it has no version or variant meaning — it is a reserved sentinel value. Developers use it as a placeholder or "none" marker: an unset foreign key, a default before a real ID is assigned, or an explicit "no entity" reference. It is the UUID analogue of null or an empty value, but still a syntactically valid 36-character UUID that fits a UUID column or type. Its opposite, the max UUID (all F's, ffffffff-ffff-ffff-ffff-ffffffffffff), is also reserved by RFC 9562 as a sentinel. This page gives you the nil value to copy directly. Free, no login.
Nil UUID = 00000000-0000-0000-0000-000000000000 — all 128 bits zero (RFC 9562)
- A reserved sentinel: no version or variant meaning, used as a "none"/placeholder marker
- Common uses: unset foreign key, default-before-assignment, explicit "no entity" reference
- Still a valid 36-character UUID that fits any UUID column or type
- The UUID equivalent of null, but syntactically a real UUID value
- Opposite sentinel — the max UUID: ffffffff-ffff-ffff-ffff-ffffffffffff (all F's), also reserved
- Copy the nil value directly above — no randomness involved
Frequently asked questions
What is the nil UUID?
The nil UUID is the special value 00000000-0000-0000-0000-000000000000, in which all 128 bits are zero. RFC 9562 reserves it as a sentinel — it carries no version or variant and represents "no UUID". It is still a syntactically valid 36-character UUID, so it can be stored in a UUID column, but its meaning is a placeholder or absence rather than an identifier of any real entity.
When would I use a nil UUID?
Use the nil UUID as an explicit "none" or default marker where a UUID is required by the type system but no real ID exists yet — for example, an unset foreign key, a field awaiting assignment, or a deliberate "no parent/no owner" reference. It plays the role that null plays for nullable columns, but it keeps the value a well-formed UUID, which can simplify schemas that do not allow nulls or that need a distinguishable default.
Is there an opposite of the nil UUID?
Yes — the max UUID, ffffffff-ffff-ffff-ffff-ffffffffffff, where every bit is one. RFC 9562 reserves it as a sentinel too, often used as an upper-bound or "highest possible" value in range queries and comparisons. Like the nil UUID, it has no version or variant meaning and exists purely as a reserved special value at the opposite end of the 128-bit range.