The use of acronyms in a Query Letter

I'm not an agent, but I wouldn't use acronyms such at that unless it was clear that I was assuming the voice of a character.

I also think clear and concise language is a must in a query letter, while keeping it in the tone of how you have written your novel.

It depends.

If BFF is consistent with the voice used in the book, and especially if this is YA or MG, I'd use it. If it isn't being used in the book, then it shouldn't be in the query.

It will limit some agents, although I'm not sure I think any agent doesn't know what BFF is, but then a book that uses a lot of texting is going to limit some agents. More obscure texting would become more problematic. As always, clarity in your query is an important goal.

Best of luck,

Jim Clark-Dawe