This tool allow to guide the user to find possible molecular formula based on a molecular formula range and a monoisotopic mass.
You may add as many elements as you want with a minimal and a maximal number of this element.
You may also add a group of atoms. For example the group C2H4O that may be present between 1 and 3 times.
For each element / group you may select if they may be present at the same time (many) or only one of them may be present (one).