https://screenrant.com/was-jimmy-an-fbi-rat-in-the-sopranos/

Jimmy Altieri was a season 1 Sopranos character who was whacked for being an FBI informant, which becomes a reflection of Tony's character.

I never thought he was, everytime some is a rat, we see them interacting with the FBI, we never see jimmy talking with them, also they call him in the middle of the night to go and see those "russian bobos" if you're a rat, that would be a major worry, you'd be looking for it, exactly like pussy was when they took up out on the boat.

But jimmy isn't nervious, he cares more about if he has enough cologne on, if you were a rat, those type of calls out of nowhere to go somewhere in the middle of the night would ring alarm bells, jimmy seems carefree.

then when silvio comes out of the ajoining room, jimmy says "don't you know i'm a captain?" in other words "you can't kill a made man" but his natural reaction if he was a rat would be "they've found out"

The reason people state for saying he was a rat is that he got off so quick when arrested by the feds, but that happened many times, it happend to sil when he was arrested at a funeral "last time i got out so quick my soup was still warm" and he did get out and back for the funeral.

Tony loved pussy so much that he was willing to convince himself it was jimmy, a theme throughout the show with tony not wanting to accept things, thats why he didn't kill tony b sooner