# UUID / GUID Decoder

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

- Page: https://decoder.tools/uuid-decoder
- Category: Identification & Serials
- Status: live, runs in the browser
- Last reviewed: 2026-10-23

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.

## Example

```text Input
01890a5d-ac96-774b-bcce-b302099a8057
```

```text Output
Version: v7
Variant: RFC 4122
Timestamp: 2023-06-30T03:34:18.518Z
```

## What is the UUID / GUID Decoder?

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.

## How to use the UUID / GUID Decoder

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

## When to use 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 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) |

## FAQ

### 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.