opening interjections: comma after yes, no, oh, and well
The comma after yes, no, oh, and well.
When yes, no, oh, or well opens a sentence, follow it with a comma: Yes, I filed it. Well, start again.
Examples
UseNo, the key is missing. (comma after the opening word)
UseWell, try the spare. (comma after the opening word)
AvoidNo the key is missing. (no comma after the opening word)