ULID Generator and Decoder
Batch-generate ULIDs or paste a list to inspect timestamp and random parts, format, and input order.
ULID Generator and Decoder
Batch-generate ULIDs or paste a list to inspect timestamp and random parts, format, and input order.
About ULID generation and decoding
Sortable IDs with monotonic batches
Each ULID starts with a millisecond timestamp encoded in the first 10 Crockford Base32 characters, followed by 16 random characters. When multiple IDs are generated in the same millisecond, the random part is incremented so the list still sorts in creation order.
Batch limit and uniqueness boundary
The page can generate up to 1,000 ULIDs at a time and uses an alphabet that avoids ambiguous characters. It is useful for sortable fixture data and database keys, but it is not a central registry that coordinates IDs across your production services.
Decode timestamp and random parts
Switch to Decode and paste one ULID per line, up to 1,000 at a time. Select a line to view the first 10 characters as a timestamp and the final 16 as the random part. Each valid entry is compared with the previous valid entry to flag adjacent duplicates or reversed input order. Invalid lines remain in place but do not participate in the order comparison. Download the JSON report to retain the decoded fields and per-line results.
FAQ
Common questions and answers about this topic.
What is a ULID?
A ULID (Universally Unique Lexicographically Sortable Identifier) is a unique ID that combines a millisecond timestamp with randomness, making it both unique and sortable by creation time.
How is ULID different from UUID?
ULID is sortable by time and uses a more compact Crockford Base32 encoding, while UUID v4 is fully random and uses hexadecimal. ULID is ideal when time-ordering matters.
When should I use ULID vs UUID?
Use ULID when time-ordering matters, such as database primary keys or event logs. Use UUID when wider compatibility with existing systems is more important.
Is my data sent to any server?
No. ULID generation and decoding run locally in your browser. Pasted IDs and decoded fields are not sent to a server, and JSON reports are created locally for download.
How do I decode a ULID and check list order?
Choose Decode and paste one ULID per line, up to 1,000. Select a line to inspect the timestamp and random part. Each valid ID is compared with the previous valid ID to flag an adjacent duplicate or reversed order; invalid lines are excluded from that comparison. The JSON report includes the decoded fields, order status, and format errors.
Does decoding verify the source or quality of a ULID?
No. It reads the encoded timestamp and random part, checks the format, and compares input order. A valid format does not verify the source, actual event time, or randomness quality. Paste one complete ULID per line; the tool does not extract IDs from arbitrary log text.