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Nil UUID Tool

Copy the nil UUID (all zeros) and the max UUID (all ones), then paste any UUID to inspect its version, variant and structure. Handy for debugging placeholder IDs and validating UUID strings in APIs and databases.

Nil and max UUID

The two special constant UUIDs.

00000000-0000-0000-0000-000000000000

Inspect a UUID

Paste any UUID to see its version and variant.

Results appear here.

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What the nil UUID is

The nil UUID is the special value 00000000-0000-0000-0000-000000000000, where every one of the 128 bits is zero. It is the UUID equivalent of a null or empty value, used as a placeholder for no ID, an uninitialized field, or a deliberately blank reference. Its counterpart, the max UUID of all f characters, marks the top end of the UUID space.

Reading version and variant

Every standard UUID carries its version in the first hex digit of the third group (1, 4, 5 or 7) and its variant in the first hex digit of the fourth group: 8, 9, a or b means RFC 4122. The inspector above decodes both fields, so you can tell at a glance whether an ID came from a timestamp, a random source or a name hash.

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Nil UUID Tool FAQs

When should I use the nil UUID?
Use it as a placeholder for an unknown or not-yet-assigned ID, for example a foreign key that has no target yet, or a default value in a form. It is clearer than an empty string because its type stays UUID.
Is the nil UUID a valid version 4 UUID?
No. Its version field is 0, which matches no defined version. Most validators accept its format but report version 0, and some strict libraries reject it as a value while accepting the format.
What is the max UUID used for?
The all-f UUID (ffffffff-ffff-ffff-ffff-ffffffffffff) is used as an upper bound in range queries, for testing sort order, and as a sentinel value meaning the end of a range.
Can I store the nil UUID in a database?
Yes, every major database accepts it as a normal UUID value. Just be aware that unique indexes treat it like any other value, so only one row can hold it per unique column.
How do I check a UUID string in code?
Match it against the 8-4-4-4-12 hex pattern with hyphens, which is what the inspector above does. Most languages also ship a parser: UUID() in Python, uuid.Parse in Go, or the uuid npm package.
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