CCs remain unchanged and should always be present, independent of the number of reaction components. They capture the identifiers and provenance of the reaction, as well as basic characteristics (reaction type, named reaction, reaction technology) and conditions (temperature, time, atmosphere, scale, concentration, stirring/shaking). Add-ons, such as the procedure or comments, also belong to the CCs. The FCs describe the more variable part of a reaction, including different starting materials, solvents, reagents, and products. Each reaction component is represented by an identifier, such as the CAS number or molecule name, a SMILES or an InChI string storing the chemical structure. While the SMILES/InChI string is available for every compound and can serve as structural input for machine learning models, the CAS number can be useful for chemists in the laboratory to order, itemize, and find chemicals. To account for starting materials and reagents, including catalysts, ligands, and additives, a third column is incorporated to specify the stoichiometric amount, that is, equivalents. SURF's flexibility enables the capture of multiple starting materials and reagents, as these can be accommodated by adding three additional columns (CAS/name, SMILES/InChI, and equivalents). If desired, further columns for additional identifiers or lot numbers can be added. As shown in Figure , the headers are populated by adding ascending numbers to record all used components. The same applies to multiple solvents or products; however, due to their role, they possess more and partly different column headers. While the CAS number/name and/or the SMILES/InChI string remain as identifiers, the solvent fraction (recorded in decimals from [0,1]) is used instead of equivalents, allowing for the exact determination of the ratio between solvents. The product category contains the largest number of headers, as the basic SURF records the reaction yield (in percent, %), complemented by the reaction yield type (i.e., isolated, LCMS, GCMS, etc.), as well as the detected mass by mass spectrometry and the nuclear magnetic resonance (NMR) spectroscopy sequence(s) in addition to the common identifiers CAS and SMILES/InChI. Additional information, such as detailed product char-Figure : The structure of the simple user-friendly reaction format (SURF). Top: Detailed structure of a SURF file, which contains constant (CC), flexible (FC), and optional columns (OC) to comprehensively capture reaction data information. Reaction components are described with two identifiers, one of them containing structural information, e.g., SMILES or InChI, and the used equivalents. For solvents, an exception applies, instead of the equivalents, the fraction is recorded (orange). In the product section, depending on the granularity required, multiple columns for product characterization can be added (blue). In the basic SURF structure, yield, yield type, nuclear magnetic resonance and mass spectroscopy information are added. Bottom: Condensed example of a SURF file that demonstrates the simple structure of the format.