How to use ULID Generator
The ULID Generator creates Universally Unique Lexicographically Sortable Identifiers right in your browser. A ULID packs a 48-bit millisecond timestamp and 80 bits of cryptographic randomness into a compact 26-character Crockford base32 string, giving you IDs that are globally unique like a UUID but also naturally ordered by creation time. Generate one or thousands at once, decode the embedded timestamp from any existing ULID, and copy the results — all locally, with nothing ever sent to a server.
- Choose how many ULIDs you want to generate using the count input.
- Click "Generate" to produce the IDs using a fresh millisecond timestamp and secure randomness.
- Copy a single ULID, or copy the whole batch with one click for pasting into code or a database.
- To inspect an existing ULID, paste it into the decode field.
- Read the decoded creation timestamp to confirm when the ID was minted.
Your data never leaves your device — 100% private processing.
What is a ULID and how is it structured?
A ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit value rendered as 26 characters of Crockford base32. The first 10 characters encode a 48-bit Unix timestamp in milliseconds, and the remaining 16 characters encode 80 bits of randomness. Because the timestamp occupies the most-significant bits and base32 preserves byte order, sorting ULIDs as plain strings sorts them by creation time. Crockford base32 deliberately excludes the ambiguous letters I, L, O and U, so the encoding is case-insensitive, URL-safe and resistant to transcription errors when IDs are read aloud or copied by hand.
| Segment | Bits | Characters | Purpose |
|---|---|---|---|
| Timestamp | 48 | 10 | Unix time in milliseconds, sortable |
| Randomness | 80 | 16 | Collision resistance within a millisecond |
| Total | 128 | 26 | Compact, URL-safe identifier |
ULID vs UUID: when should you choose each?
A UUIDv4 is 128 bits of pure randomness rendered as 36 hex characters with hyphens. It is excellent for uniqueness but its random layout means new rows scatter across a B-tree index, hurting insert performance and making natural ordering impossible. A ULID keeps the same 128-bit uniqueness budget but front-loads a timestamp, so inserts append near the end of the index and rows sort chronologically for free. Choose a ULID when you want database-friendly, time-ordered keys or human-readable correlation IDs. Stick with a UUID when you need a widely standardised format, when ordering could leak sensitive timing information, or when an existing system mandates the RFC 4122 layout.
Worked examples
Generate a single ULID
Inputs: Count: 1
Result: 01ARZ3NDEKTSV4RRFFQ69G5FAV
Decode a ULID timestamp
Inputs: 01ARZ3NDEKTSV4RRFFQ69G5FAV
Result: Created 2016-07-30T23:54:10.259Z
Glossary
- ULID
- A 128-bit, 26-character identifier combining a millisecond timestamp with random bits so that IDs are both unique and lexicographically sortable.
- Crockford base32
- A base32 alphabet that omits the ambiguous characters I, L, O and U, making encoded values case-insensitive and safe to read aloud.
- Lexicographic sort
- Ordering strings character by character; for ULIDs this coincides with chronological order because the timestamp comes first.
- Monotonicity
- A ULID property where IDs generated within the same millisecond can increment the random component to preserve strict ordering.
- Entropy
- The 80 random bits in a ULID that make collisions astronomically unlikely even at high generation rates.
Related reading
Frequently Asked Questions
Why use ULID Generator?
- Generate time-sortable IDs that order correctly in databases and logs without an extra timestamp column
- Produce shorter, URL-safe identifiers (26 chars vs 36 for a UUID) with no special characters
- Bulk-generate hundreds of ULIDs in a single click for seeding or load testing
- Decode the creation timestamp embedded in any ULID for debugging and auditing
- Runs entirely client-side using the Web Crypto API, so generated IDs never touch a server
Common use cases
- Primary keys for database rows that should sort chronologically without a separate created_at index
- Correlation IDs in distributed logs and traces that you can sort and time-bucket directly
- File or object storage names where lexical order matches upload order
- Event IDs in append-only event-sourcing systems that need natural ordering
- Seeding test data with realistic, ordered identifiers during development
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