ULID Generator

Create lexicographically sortable ULIDs that embed a millisecond timestamp. Click Run with empty input for one ULID, or enter a count (1–50) for batch generation.

  • Runs entirely in your browser
  • No data stored or sent to a server
  • Free forever — no signup
  • Instant conversion

Input and Output

Use the interactive encoder and decoder on this page to process your text.

Learn more about ULID generation

How to Generate ULIDs

ULID Generation

When to Use ULIDs

Choose ULIDs when you need unique IDs that sort chronologically — event logs, database primary keys with good B-tree locality, distributed tracing spans, or any system where time-ordered IDs improve query performance over random UUIDs.

Real-World Examples

Log entry ID: 01ARZ3NDEKTSV4RRFFQ69G5FAV — first 10 chars encode timestamp

Primary key in a table where recent rows are queried most often

Message queue deduplication keys with natural time ordering

Common Mistakes

  • Assuming ULIDs are UUIDs — they are a different 128-bit format using Crockford Base32
  • Generating multiple ULIDs in the same millisecond without monotonic increment logic (this tool uses random suffixes)
  • Case-sensitive comparisons — ULIDs use uppercase Crockford alphabet (no I, L, O, U)

Edge Cases

  • ULIDs from the future (clock skew) sort after current-time IDs
  • 26 characters, URL-safe, no hyphens — do not confuse with 24-char ObjectIds
  • Timestamp precision is milliseconds — sub-millisecond ordering is not guaranteed without monotonic mode

Developer Tips

  • Libraries: ulid npm package for Node.js with monotonic support
  • Extract timestamp: decode first 10 Crockford Base32 chars as 48-bit milliseconds since Unix epoch
  • Prefer ULIDs over UUID v4 when index fragmentation is a concern

Frequently asked questions

What is the difference between ULID and UUID?

ULIDs are 128-bit identifiers encoded as 26 Crockford Base32 characters. The first 48 bits are a timestamp, making them lexicographically sortable. UUIDs are 36-character hex strings and v4 UUIDs are random, not time-ordered.

Can I generate multiple ULIDs at once?

Yes. Enter a count between 1 and 50, or leave the input empty to generate one ULID.

Are ULIDs URL-safe?

Yes. ULIDs use Crockford Base32 encoding with only uppercase letters and digits — no special characters, hyphens, or padding.