Guide
How Time-Ordered UUID v7 and ULID Identifiers Work
Understand why time-ordered IDs are useful, how UUID v7 and ULID encode time, and when to prefer them.
Updated September 8, 2026
UUID v7 and ULID are time-ordered identifiers: they embed a timestamp so that IDs generated in sequence sort naturally by time. A generator creates them on demand for databases and distributed systems.
Why time-ordered IDs matter
Random UUIDs (v4) are unique but unordered — inserting them into a database index causes random page writes and fragmentation. Time-ordered IDs sort monotonically, so new rows append to the end of the index, which is faster and more compact. They are also easier to debug because you can tell creation order at a glance.
UUID v7 vs. ULID
UUID v7 (RFC 9562) puts a 48-bit Unix millisecond timestamp in the high bits and fills the rest with random bits, producing a 128-bit UUID that sorts by time. ULID (Universally Unique Lexicographically Sortable Identifier) does the same idea but encodes the result as a 26-character Crockford base-32 string, which is shorter and URL-safe. Both sort lexicographically by creation time.
How to use the generator
- Choose UUID v7 or ULID.
- Choose how many to generate.
- Copy the identifiers for use as keys.
Examples
A UUID v7 like 0190f5c3-... starts with the timestamp, so a list of v7 IDs generated minutes apart sorts in creation order. A ULID like 01ARZ3NDEKTSV4RRFFQ69G5FAV sorts the same way and is 26 characters instead of 36.
When to prefer time-ordered IDs
- Database primary keys where insert order matters.
- Event logs and audit trails that should sort by time.
- Distributed systems needing unique, sortable ids.
- URL-friendly identifiers (ULID especially).
Put it into practice
Use the UUID v7 / ULID Generator right now — free, in your browser, no sign-up required.
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