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Comment by zaken

1 year ago

I tried to find the biggest UUID and if I got it right, it's

99999999-9999-4999-9999-999999999999

(note the 4 in the 3rd block)

I'm curious why it's not 99999999-9999-9999-9999-999999999999 (all 9s)?

20 comments

zaken

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dmlittle  1 year ago

It depend on the UUID version you're using. Version 4 (Random) will always have that value be 4 as per RFC 9562. So 99999999-9999-9999-9999-999999999999 is a valid UUID but not a valid UUID v4. If you wanted to be pedantic the website should have been named https://everyuuidv4.com/

https://datatracker.ietf.org/doc/html/rfc9562

savef  1 year ago

The values are hexidecimal, so all "9s" isn't the biggest UUID, but all "f's". Specifically, I think: `ffffffff-ffff-4fff-bfff-ffffffffffff`.

The "4" in the 3rd block is the only permitted value as these UUIDs are using the GUIDv4 format. I'm not sure what's going on in the 4th block, but the references and linked RFC in the Wikipedia article might reveal more details: https://en.wikipedia.org/wiki/Universally_unique_identifier#...

  • Dylan16807  1 year ago

    If you're going by hex, the biggest UUID is entirely f's, 32 of them. It's defined specially and doesn't have version or variant.

    • savef  1 year ago

      I see what you mean, but I was going by the definition of "UUID" used on everyuuid.com. The UUID of 32 "f's" isn't in the list.

      1 reply →

  • MBCook  1 year ago

    But if it’s all Fs, that means you have the sign bit set, so it’s not the largest.

    It’s the smallest that’s less than zero right?

Dylan16807  1 year ago

Looks like it only generates v4 UUIDs, which is a bit of a ripoff.

Also you'll find that the first character of the 4th block is forced to be 8, 9, a, or b. That's true of standard UUIDs of any version.

ajsfoux234  1 year ago

The 4 indicates UUIDv4.

If you were looking for the biggest hexadecimal UUID, find one with f instead of 9.