Three sets: read a structure and write its SMILES, read a SMILES and draw the structure, or write a SMARTS pattern that tells two molecules apart. Every answer is marked in the browser, against the structure rather than against a stored string, so a different correct spelling is still correct.
Convert between chemical structures and SMILES in both directions, search a list of structures by substructure or SMARTS, and learn the notation step by step. Everything runs in your browser — no structure you open ever leaves your machine — so the tool needs JavaScript.