The Modifier Tone Letters block spans U+A700–U+A71F, 32 codepoints in Plane 0 (Basic Multilingual Plane). Every one of them is assigned in Unicode 16.0.
All of its characters have the script value Common: they are shared across writing systems rather than tied to one.
By general category: 23 modifier symbols (Sk), 9 modifier letters (Lm).
The first 23 arrived in Unicode 4.1 (2005); later additions came in 5.0 (4), 5.1 (5).