They're both acceptable in English. The rule is generally "an" if the following word starts with a vowel. But, it gets a bit tricky with initialisms (like URL) because URL is normally pronounced something like "you-are-ell", and not "earl". So the spelling starts with a vowel, but the pronunciation doesn't. Nobody would fault you for using one or the other in a situation like this.

[–] Valmond@lemmy.ml 3 points 1 year ago (1 children)

TIL, I always thought the sound made the law (so a URL but not an URL)

[–] 133arc585@lemmy.ml 2 points 1 year ago

I'm sure some style guide(s) have hard and fast rules but being called out for it in everyday conversation doesn't (shouldn't) happen for something like that. English also isn't French, it doesn't have a regulatory body, and so attempting to pin down certain things as definitively correct or definitively wrong isn't always a reasonable thing to do.

[–] BlessedDog@lemmy.ml 1 points 1 year ago

Oh okay thank you :)