ULID Generator

About ULID Generator

The ULID Generator creates Universally Unique Lexicographically Sortable Identifiers, a modern alternative to UUID/GUID. A ULID is a 26-character Crockford Base32 string encoding a 48-bit millisecond timestamp followed by 80 bits of randomness — making ULIDs globally unique while sorting chronologically by default. Unlike UUID v4, ULIDs embed a time component, so a sorted list of ULIDs is also sorted by creation time. They are URL-safe, case-insensitive, and monotonically sortable when multiple are generated within the same millisecond. ULIDs are widely used as primary keys in distributed systems, event logs, and databases where insertion order matters.

Why use ULID Generator

How to use ULID Generator

1. Click Generate to create a new ULID.
2. Use the Count field to generate multiple ULIDs at once.
3. Click Copy to copy a single ULID or Copy All for the full batch.
4. The timestamp component is decoded and displayed so you can verify the embedded time.
5. Switch on Monotonic mode if you need multiple ULIDs in one millisecond to maintain strict insertion order.
6. Pick a custom timestamp to generate historical ULIDs for backfilling records or simulating time-travel test data.

When to use ULID Generator

• Generating primary keys for database records where insertion order should be sortable.
• Creating event IDs in distributed logs where time ordering is needed.
• Replacing UUID v4 when lexicographic sort order matters.
• Generating batch IDs for imports, jobs, or distributed tasks.
• Building append-only event stores or audit logs where range queries by time are common.
• Sharding data across nodes when you want recent rows to colocate naturally on the same partition.

Examples

Tips

• Generate a batch and inspect the IDs side by side — within the same millisecond, ULIDs incremement monotonically so you can verify the random suffix is sorted, not just the timestamp prefix.
• Treat the 26-character ULID as opaque in your application code; do not slice the string to extract the timestamp manually because edge cases at the 48-bit boundary will bite you.
• Store ULIDs as a 16-byte BINARY(16) column in MySQL or BYTEA in Postgres for index density — VARCHAR storage works but doubles the size and slows range scans.
• When inserting many rows in a tight loop, reuse a monotonic ULID factory rather than calling Generate per row to keep ordering stable inside one millisecond bucket.
• ULIDs are case-insensitive, but always normalize to uppercase on write so that clustered indexes stay tight and string comparisons remain stable across drivers.
• Avoid mixing ULIDs and UUIDs in the same primary-key column — Crockford Base32 and hex-with-dashes have different sort orders and any join you build will misbehave.
• If you expose ULIDs in URLs, audit for ID-enumeration risk; the timestamp prefix leaks creation time, which can be a privacy concern for user-facing resources.

Frequently Asked Questions

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Glossary

ULID

Universally Unique Lexicographically Sortable Identifier — a 128-bit ID encoded as 26 Crockford Base32 characters with a 48-bit timestamp prefix.

Crockford Base32

An alphabet of 32 characters (0-9, A-Z minus I, L, O, U) designed by Douglas Crockford to be unambiguous when read or transcribed by humans.

Lexicographic sortability

The property that sorting strings as text yields the same order as sorting them as creation timestamps; ULIDs are designed to satisfy this.

Monotonicity

Guarantee that two IDs generated in the same millisecond still sort correctly — implementations achieve this by incrementing the random component.

Time component

The first 48 bits (10 characters) of a ULID, encoding Unix milliseconds since 1970, valid through the year 10889 AD.

Random component

The trailing 80 bits (16 characters) of a ULID, drawn from a cryptographically secure RNG to give 2^80 unique values per millisecond.

Collision probability

Chance that two independently generated IDs are identical; for ULIDs, requires more than 2^40 IDs in one millisecond before collisions become likely.