What is the rule for using 'a' or 'an' before words starting with 'j'?

What is the rule for using 'a' or 'an' before words starting with 'j'?

The rule for using 'a' or 'an' before words starting with 'j' is to use 'an' before words that have a silent 'j' sound, such as "an hour" or "an honest person." Use 'a' before words that have a pronounced 'j' sound, such as "a jacket" or "a job."