ULID Generator

The ULID Generator creates Universally Unique Lexicographically Sortable Identifiers (ULIDs) entirely in your browser. ULIDs combine the benefits of UUIDs with timestamp-based sorting, making them ideal for distributed systems, database keys, and event logging. For other unique identifier needs, try our UUID Generator Tool or Random String Generator.

How to use the ULID Generator?

Select the number of ULIDs you want to generate (1-100) using the quantity input, then choose between raw format (one ULID per line) or JSON array format. The ULIDs update automatically when you change the settings. Use the Refresh button to generate new values or the Copy button to copy them to your clipboard.

What is a ULID?

A ULID (Universally Unique Lexicographically Sortable Identifier) is a 26-character identifier that encodes a 48-bit timestamp (millisecond precision) followed by 80 bits of random data. ULIDs are case-insensitive, use Crockford's base32 encoding (no ambiguous characters like I, L, O, U), and are designed to be collation-friendly for database indexing.

ULID vs UUID

ULIDs offer several advantages over traditional UUIDs: they are lexicographically sortable by time, more URL-friendly with their 26-character Crockford base32 encoding (vs 36-character UUID hex), and have a more readable format. However, UUIDs remain the standard choice when backward compatibility or strict RFC 4122 compliance is required.

Common Use Cases

ULIDs are commonly used as primary keys in distributed databases, event stream identifiers in event sourcing architectures, log entry IDs in logging systems, order identifiers in e-commerce, and message IDs in message queues. Their time-sortable nature makes them especially valuable for time-series data and audit trails.

Are ULIDs cryptographically secure?

ULIDs use random data for the non-timestamp portion, but they are not designed to be cryptographically secure. The random component uses standard Math.random() which is adequate for identifier generation but should not be used for security-sensitive applications.

Can ULIDs be decoded to reveal timestamps?

Yes, the first 10 characters of a ULID encode the timestamp in Crockford base32. You can decode this to retrieve the creation time in milliseconds since the Unix epoch. This is by design, as ULIDs are meant to be time-sortable.

Are ULIDs unique?

ULIDs produce 80 bits of randomness (1.21 x 10^24 possible values per millisecond), making collisions extremely unlikely in practice. For most applications, the probability of collision is negligible even at high generation rates.

What is the difference between raw and JSON format?

Raw format outputs one ULID per line, which is useful for direct use in scripts or terminal commands. JSON format wraps the ULIDs in a JSON array structure, making it suitable for programmatic consumption in applications and APIs.

Can I use ULIDs in my database?

Yes, many databases support ULIDs as primary keys. Their lexicographic ordering makes them efficient for B-tree indexes, and the timestamp prefix allows for chronological ordering without a separate timestamp column. Some databases offer native ULID types or you can store them as VARCHAR(26).