Engineering
ULID Identifiers: When to Use Them in Your Software
Understand how ULIDs combine timestamps and randomness, when sortable identifiers help, and what to consider before using them in your application.
Retenvo Team ·
Choosing a record identifier affects database design, API URLs and the way teams investigate problems. A useful starting point is deciding whether IDs must be generated independently and whether their ordering should reflect creation time.
What is a ULID?
A ULID is a 128-bit identifier represented as 26 characters. It combines a 48-bit millisecond timestamp with 80 bits of randomness. Its encoded form is lexicographically sortable, so ordinary string ordering groups identifiers by their timestamp. These properties are defined in the canonical ULID specification.
The timestamp also makes approximate creation time visible. A ULID should never act as a password, access token or proof that someone is allowed to read a record.
Where sortable IDs can help
Consider identifiers generated across several application processes, or public references that support staff need to locate in logs. Before selecting a format, write down the operational problem it should solve. Independent generation and sortable references are useful requirements; they do not automatically make one format the right choice for every table.
Decisions to make before implementation
- Check your database column type, indexing and comparison behavior.
- Choose a maintained library that implements the specification, including overflow handling.
- Decide whether generation within the same millisecond needs the specification’s monotonic behavior.
- Keep an explicit creation timestamp for reporting and use the correct business timestamp for event ordering.
- Apply authorization checks to every record lookup, regardless of the identifier format.
For an existing application, plan migration around foreign keys, integrations and public URLs. A new identifier format should solve a concrete requirement without breaking references customers already use.
If you are designing a new platform, our custom software development team can help define its data model, APIs and integration requirements. See our development process for how we move from discovery to delivery.