What is a UUIDv7?
UUIDv7 is a time-sortable UUID format defined in RFC 9562. Unlike UUIDv4, which is entirely random, UUIDv7 embeds a 48-bit Unix timestamp (milliseconds since epoch) in the most significant bits, followed by random data. This means UUIDv7s created later will always sort after earlier ones when compared lexicographically.
The format is
tttttttt-tttt-7xxx-yxxx-xxxxxxxxxxxx,
where the t
positions carry the Unix timestamp in milliseconds,
7
indicates the version, and
y
is one of 8,
9,
a, or
b
(the RFC 4122 variant bits). The remaining positions are filled with cryptographically secure random data.
UUIDv7 vs UUIDv4
| Feature | UUIDv4 | UUIDv7 |
|---|---|---|
| Sortable | No | Yes (by creation time) |
| Embeds timestamp | No | Yes (48-bit Unix ms) |
| Random bits | 122 bits | 74 bits |
| Database index performance | Poor (random order) | Good (monotonically increasing) |
| RFC | RFC 4122 | RFC 9562 |
| Version digit | 4 | 7 |
When to Use UUIDv7
UUIDv7 is a strong choice when you need the uniqueness guarantees of a UUID but also want natural time ordering. Common use cases include:
- Database primary keys where B-tree indexes benefit from sequential inserts rather than random scatter.
- Event sourcing and logs where events should be naturally ordered by creation time without a separate timestamp column.
- Distributed systems where multiple nodes generate IDs independently but you still want a rough global ordering.
- Message queues where consumers process messages in approximate arrival order using the ID alone.
If you don't need time ordering and want maximum randomness, UUIDv4 remains the simpler option.
Frequently Asked Questions
- How does UUIDv7 encode the timestamp?
- The first 48 bits (the 12 hex characters before the version nibble) store the number of milliseconds since the Unix epoch (January 1, 1970). This gives UUIDv7 a usable range well past the year 10,000.
- Can I extract the creation time from a UUIDv7?
- Yes. The validator above automatically extracts and displays the embedded timestamp when a valid UUIDv7 is detected. You can also do this programmatically by reading the first 48 bits as a big-endian integer and interpreting it as Unix milliseconds.
- Are UUIDv7 IDs guaranteed to be strictly monotonic?
- UUIDv7s generated within the same millisecond on different machines may not be strictly ordered relative to each other, since the sub-millisecond portion is random. Within a single process, implementations can use a counter or monotonic random sequence to guarantee strict ordering.
- Does UUIDv7 leak timing information?
- Yes, the embedded timestamp reveals when the UUID was created down to the millisecond. If creation time is sensitive in your application, UUIDv4 (fully random) is the better choice.
- Is my data sent to a server?
- No. UUIDs are generated and validated entirely in your browser using the Web Crypto API. Nothing is sent to any server.