ULID Generator — Sortable Unique Identifiers

• ULIDs are 128-bit identifiers encoded as 26-character Crockford Base32 strings
• Lexicographically sortable — ULIDs created later sort after earlier ones
• First 10 characters encode millisecond timestamp, last 16 are random
• Drop-in replacement for UUIDs with better sorting and readability
• No special characters — safe for URLs, filenames, and databases

Use Cases

Frequently Asked Questions

What is the difference between ULID and UUID?

ULIDs are lexicographically sortable by creation time (timestamp prefix), while UUID v4 is fully random. ULIDs are 26 characters with no hyphens; UUIDs are 36 characters with hyphens. Both are 128-bit identifiers.

Can I use ULID as a database primary key?

Yes, and it is often better than UUID v4. ULID's time-ordered prefix means inserts are sequential in B-tree indexes, reducing page splits and improving write performance in PostgreSQL and MySQL.

Are ULIDs unique enough for production?

Yes. Each millisecond has 80 bits of randomness (2^80 possible values), making collisions practically impossible even in high-throughput distributed systems.

Can I extract the timestamp from a ULID?

Yes. The first 10 characters encode a 48-bit millisecond timestamp. Most ULID libraries provide a function to extract the creation timestamp from any ULID.

Should I replace all UUIDs with ULIDs?

Consider ULIDs when you need sortable IDs (database keys, event streams). Keep UUIDs for existing systems where changing ID format would require migration, or when you need RFC 4122 compliance.

Is ULID compatible with UUID columns in databases?

ULIDs are 128 bits and can be stored in UUID columns by converting to the standard 8-4-4-4-12 format. Many ULID libraries support this conversion natively.