UUID v7 Generator
A version 7 UUID is ready as the window opens: its first 48 bits are the time in milliseconds, so IDs made later sort later, as text and as bytes. Make one or a thousand, copy them as lines, a JSON array or an SQL list, and paste any v7 into Inspect to read when it was made.
What it does
- RFC 9562’s layout: 48 bits of Unix milliseconds, the version digit 7, a 12-bit counter, the variant, and 62 random bits.
- The counter keeps IDs from one millisecond in order: a thousand made at once still sort as they were made.
- The counter starts low enough to leave room for 2,048 more IDs, so a batch never runs out within a millisecond.
- The standard, no-hyphen and upper-case forms keep the time order as text; the 22-character Base64URL form does not.
- Inspect reads a v7 back to the time it was made, in UTC and to the millisecond.
- Within a batch a clock that steps back is not followed, so no ID sorts before the one made ahead of it.
How to use it
- Set how many, from one to a thousand.
- Pick the form: standard, no hyphens, braces, URN or Base64URL.
- Copy them, or download them as lines, a JSON array or an SQL list.
- Paste a v7 into Inspect to read the time it was made.
What it does not do
- Hiding when a record was made: the time is in the ID for anyone to read, so IDs shown to the public may be better as version 4.
- Order between machines: each orders its own IDs, and two clocks a few milliseconds apart interleave theirs.
Questions
Why use version 7 for a primary key?
New keys land at the end of the index instead of at random places in it, so a B-tree index stays compact and an insert touches fewer pages. Version 4 keys scatter the writes across the whole index as the table grows.
Can I read the time inside a UUID v7?
Yes. The first 12 hex digits are the milliseconds since 1970: paste the UUID into Inspect and the time appears in UTC. One that starts 018bcfe5-6800 was made on 14 November 2023 at 22:13:20 UTC.
Is a UUID v7 as unique as a v4?
Close to it. Each carries 62 random bits, and its counter starts at a random value, and two IDs can only clash when they share a millisecond. A v4 has 122 random bits and no time at all.
Do databases sort them by time?
A native uuid column compares the bytes in order, and so does a text column holding the standard form, so both sort by time. SQL Server’s uniqueidentifier is the exception: it compares the last six bytes first.
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