What this tool computes, and how far to trust it: the geometries come from openchemlib’s torsion-driven generator and MMFF94, which is springs and point charges with no electrons in it, so a relative energy orders the shapes rather than measuring them.
The 3D view is Mol*, the optional refinement is GFN2-xTB compiled to WebAssembly, and all of it runs in the page.
Conformers in 3D from a structure you draw. This tool needs JavaScript; these are the pages it offers: