Type a formula and the isomers are enumerated one by one, counted as they come. Surge itself runs as WebAssembly in the page, so a formula with hundreds of thousands of isomers costs your own tab rather than a server.
Constitutional isomers are the structures a formula allows: the same atoms bonded differently. Stereoisomers are not among them, which is why the count is smaller than the number of distinct molecules.
Type a molecular formula and get every constitutional isomer of it, enumerated by Surge running as WebAssembly in your browser — so nothing is uploaded and nothing is queued. The tool therefore needs JavaScript.