What's Reliable Here
Drawing, formula, molecular weight, exact (monoisotopic) mass, SMILES and molfile output are handled by OpenChemLib, an established open-source cheminformatics library, running entirely in your browser. Degree of unsaturation is computed from the atom counts for neutral structures with normal valences. cLogP, logS and TPSA are OpenChemLib's calculated estimates. They are fine for screening and comparing structures, not a substitute for measured data.
Lipinski's rule of 5 counts H-bond donors as NH/OH groups and acceptors as N and O atoms; one violation is conventionally still considered acceptable. Veber's rules (rotatable bonds ≤ 10, TPSA ≤ 140 Ų) are a complementary oral-bioavailability check.
Known Limitations
IUPAC names, InChI and InChIKey are not generated locally. They come from PubChem, and only when you press the lookup button (which sends the structure's SMILES to PubChem). Loading by compound name also uses PubChem. Structures you draw are remembered only in this browser, on this device.