Mac Pro Tip: macerror

Ran across an obscure error code working on an iOS app at my day job. It turns out there's a utility on the Mac that will give you a little more to go on than some random negative integer: simply run

macerror [error code]

to get a (slightly) more descriptive version. For instance, I was getting error code -25299 trying to add an entry to my app's keychain; macerror reports that as errKCDuplicateItem.