A lot people use "agreed" as an interjection, especially while writing comments in blogs, forums, and other online platforms. This use is also mentioned by different English dictionaries (e.g. Collins), but I don't know whether it can be used in a more formal setting than an online forum.
I'm also curious as to its actual meaning.
Is it a shorthand of I have agreed? If so, is the present perfect used (albeit in an abbreviated form) to describe an action that was completed in a very recent past?
Or is it a shortand of I am agreed? I sometimes find this expression, although in a different setting than "agreed", but I'm not sure it is correct.
Or is it something else entirely? I've tried searching on the Internet, but I haven't found an answer so far.