Among the existing well-designed traditional browser-based 2D molecule editors such as JSME and MarvinSketch , we chose Kekule.js for its ease of integration as a web application and its sufficient functionality. Its JavaScript-based editor can input and output SMILES strings and CML strings of manually drawn structural formulas. While SMILES only stores simple characters to express atoms, bonds, rings, and their orders, CML has coordinate and rotation information of each atom and bond. Furthermore, CML contains many XML markup tags in addition to that information. Meanwhile, CML strings become too long to tweet because one tweet accepts only 280 characters. However, URL strings are not included in this limitation. To embed CML strings into an URL, chemical.space/editor compresses CML strings by gzip using pako library, then encodes it into Base64url using brianloveswords/base64url .