ULID generator
A ULID is a 128-bit identifier written as 26 characters that sort in the order they were created. Generate a batch here, or paste a ULID to see the exact time it encodes.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose how many ULIDs you need and copy the list.
- Press Generate again for a new batch.
- To check an existing id, paste it into the decode box to see its timestamp in UTC.
How it works
The first 10 characters encode the Unix time in milliseconds. Each character is 5 bits of a base32 number, so the example 01ARYZ6S41 is 1469918176385 ms, which is 2016-07-30T22:36:16.385Z. The last 16 characters are 80 random bits from crypto.getRandomValues.
Tips
- Lowercase is only a display choice; the value is the same.
- ULIDs make good database keys because new rows land at the end of the index.
- The timestamp field holds 48 bits, so the format works until the year 10889.
Frequently asked questions
What is a ULID?
A Universally Unique Lexicographically Sortable Identifier. It has a 48-bit timestamp in milliseconds followed by 80 random bits, written in Crockford base32 as 26 characters. Sorting ULIDs as text sorts them by creation time.
How is a ULID different from a UUID?
Both are 128 bits. A ULID is shorter as text (26 characters against 36), uses no hyphens, and always starts with the time. UUID version 7 also starts with the time but is written in hex with hyphens.
Why is there no I, L, O or U?
Crockford base32 leaves them out because they are easy to confuse with 1 and 0, and U is skipped to avoid accidental words. When decoding, this tool accepts upper or lower case.
Are ULIDs created in the same millisecond still in order?
Yes. Following the ULID specification's monotonic mode, each further ULID in one batch adds one to the random part of the previous one, so the list is strictly increasing.
Does a ULID hide when it was made?
No. The first 10 characters are the creation time and anyone can decode it, so do not use a ULID where the creation time must stay private.