On: Airlines are running out of 4-digit flight numbers

[lxgr]

I could imagine many legacy systems identifying “their” flights based on the alphanumeric prefix alone (as opposed to doing a database lookup).

[globular-toast → lxgr]

Yep. Not only a ton of software would make this assumption, but a ton of human-based processes too.

Lesson: if you make your IDs easily decodable, people will decode them and use them directly instead of whatever API you intended them to use.

[Schiendelman → globular-toast]

That's what happens with requisition numbers for jobs! If they're too short (12345), recruiters remember them, start building manual processes dependent on them, and then when they collide with others on a job board (like Indeed, or if the employer hires an agency to help) you end up needing a parallel identifier...

[lxgr → globular-toast]

According to Hyrum's law, this is an API :)