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Editorial Team
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Asked: 2026-05-20T16:49:50+00:00

I need a 6 character alphanumeric ID for use in my rails app, which

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I need a 6 character alphanumeric ID for use in my rails app, which will be presented to users of the system and must be unique among all the object instances in my system. I don’t expect more than a few thousand object instances, so 6 characters is far more than I really need.

At this point I’m using the UUIDTools gem in my Rails app to generate a uuid. Which of the UUIDTools generation methods should I use, and which end of the resulting uuid should I take the 6 characters from, to guarantee uniqueness?

for example, if I generate ef1cf087-95c9-4868-bd95-cea950a52b58, would I want to use ef1cf0 from the front of it, or a52b58 from the back end?

… as a side note / question: am i going about this wrong? is there a better way?

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  1. Editorial Team

    No way. UUID is considered unique because it is very long and it is practically impossible to generate same UUIDs. If you trim it to 6 chars then you drammatically increase possiblility of duplicate. You have to use either incrementing id or full UUID.

    Only deterministic generation (id(x + 1) = id(x) + 1) can guarantee uniqueness. UUID doesn’t guarantee it and 6 chars guarantee it even less.

    Other option is to create ID generation service, it will have single method getNewId and will keep knowledge that will be enought to provide unique ids. (Simplest case – counter)

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