ULID Generator
Generate lexicographically sortable ULIDs with timestamp entropy.
ULID Generator
What This Tool Does
- ULID Generator creates universally unique, lexicographically sortable identifiers with millisecond-precision timestamps.
- Generate time-ordered unique IDs perfect for event logs, database records, and distributed systems needing natural ordering.
Usage
- Set quantity: generate one or multiple ULIDs.
- ULIDs are created with current timestamp and random entropy.
- Copy results into logs, event tables, or distributed systems.
- Review the sortable order: ULIDs generated later sort higher than earlier ones.
Examples
- Generate ordered event IDs for event sourcing and replay simulations.
- Create identifiers for database records that naturally sort by creation time.
- Produce trace IDs for request tracing in microservices (sortable by arrival time).
- Generate order or transaction IDs that sort by initiation time without separate timestamps.
Limitations
- Results should be validated in your target runtime before production use.
- Extremely large input payloads may be constrained by browser memory and performance limits.
Common Mistakes
- Sorting ULIDs as strings without Crockford Base32 awareness: ULID strings are sortable correctly, but custom parsing may break.
- Assuming constant sortability across systems: Clock skew between systems breaks sort order. Sync time between services.
- Losing leading zeros in string conversions: ULID strings may start with 0; preserve leading zeros when storage/conversion.
- Comparing ULIDs after encoding/decoding: Always compare in same format (Base32 string or binary). Mismatched formats break comparisons.
- Using ULID where UUID standardization required: Older systems expect UUID format (RFC 4122). Use UUID for interop.
- Monot onic monotonicity not guaranteed across process restarts: ULID monotonicity per process. Restart may reset counter.
Technical Reference Guide
- ULID: Universally Unique Lexicographically Sortable Identifier.
- Format: 48-bit timestamp (milliseconds since epoch) + 80-bit random data = 128 bits total.
- String representation: 26-character Crockford Base32 encoding (0-9, A-V, no I, L, O, U for readability).
- Sortable: Lexicographic (alphabetical) ordering matches creation time order. No post-processing needed.
- Monotonic: When multiple IDs generated in same millisecond, random portion increments to maintain order.
- Timestamp: Millisecond precision. Epoch year 5235 before overflow (10,000+ year horizon).
- Entropy: 80 bits random ≈ 2^80 combinations per millisecond, collision probability negligible.
Specifications & Standards
FAQ
How is ULID different from UUID?
ULIDs are lexicographically sortable by timestamp (first 48 bits) while preserving randomness. UUIDs are unordered. ULIDs are shorter (26 vs 36 chars).
Are ULIDs guaranteed unique?
Probabilistically unique. Collision probability for 80-bit randomness per millisecond is negligible (< 1 in 10^24). Sequence guarantee within same millisecond via monotonicity.
Can ULIDs be decoded to extract timestamp?
Yes, if you have a ULID decoder. First 48 bits = milliseconds since Unix epoch. Use a ULID library to extract cleanly.
What if two ULIDs are generated in the same millisecond?
The random portion increments to maintain monotonic ordering (ULID spec). This ensures ULIDs from same service stay ordered even at identical timestamps.
Do ULIDs work across distributed systems?
Yes, but only if services have synchronized clocks. Clock skew breaks sort order. Use NTP or similar for time sync.
Should ULIDs be used as database primary keys?
Yes, they are excellent for distributed databases. Natural sort order improves index efficiency and query performance.
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