The National Library of Medicine (NLM) is the world's largest medical library. The Library collects materials and provides information and research services in all areas of biomedicine and health care. The ChemSpell Web Service API provides chemical name spell checking and chemical name synonym look-up. ChemSpell contains more than 1.3 million chemical names related to organic, inorganic, pharmaceutical, toxicological, and environmental health topics. Developers can use the API to write applications that connect remotely to the ChemSpell Web service. The API uses SOAP calls and responses are formatted in XML.