How do I tell which UUID version I have?

The first character of the third group is the version digit: 1, 4, 5 and 7 are the ones you meet in practice. This decoder reads it and the variant bits for you.

Can a UUID be reversed to reveal information?

v1 exposes its creation timestamp and the generating machine's MAC address, and v7 exposes a millisecond timestamp. v4 is random and reveals nothing at all.

Should I use UUID v4 or v7 for a database key?

v7, in most cases. Its time-ordered prefix keeps inserts sequential and preserves index locality, whereas v4's randomness scatters writes across the B-tree and hurts performance at scale.

Are UUIDs really unique?

For practical purposes, yes. v4 has 122 random bits — you would need to generate billions per second for many years before a collision became likely.

UUID / GUID Decoder

Read a UUID's version, variant and — where present — its embedded timestamp.

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RAW INPUT

DECODED

Output appears here as you type — decoded on your device.

Input is processed on your device. Nothing you paste is sent anywhere.

What is the UUID / GUID Decoder?

A UUID decoder inspects a 128-bit universally unique identifier to determine which version generated it, what its variant bits say about its layout, and whether it carries a recoverable timestamp or node identifier.

A UUID is 128 bits written as 32 hex digits in five dash-separated groups. Two fields describe its own structure: the version nibble (the first character of the third group) and the variant bits (the first character of the fourth group, normally 8, 9, a or b for the RFC 4122 layout).

The versions differ in what they encode. v1 embeds a 60-bit timestamp and the generating machine's MAC address — which is why a v1 UUID leaks both creation time and host identity. v4 is 122 bits of randomness and reveals nothing. v5 is a SHA-1 hash of a namespace and a name, so the same input always yields the same UUID. v7, standardised in RFC 9562, puts a Unix millisecond timestamp in the leading bits, making it time-sortable — the property that makes it a far better database primary key than v4, whose randomness fragments B-tree indexes.

Decoding tells you which of these you have, and for v1 and v7 recovers the creation time.

UUID / GUID Decoder at a glance

Size: 128 bits · 32 hex digits · 36 characters with dashes
v4: Random — 122 bits of entropy, no metadata
v1: Timestamp + MAC address — leaks time and host
v7: Unix ms timestamp first — time-sortable (RFC 9562)

How to use the UUID / GUID Decoder

1Paste the UUID, with or without dashes or surrounding braces.
2Read the detected version and variant.
3For v1 and v7, read the recovered creation timestamp.

When you would reach for it

Working out when a v1 or v7 record was created from its identifier alone.
Confirming a library generates the UUID version you configured.
Choosing between v4 and v7 for a new table's primary key.

UUID / GUID Decoder — frequently asked questions

Last reviewed 25 July 2026 · questions or corrections: contact@decoder.tools