The first public version of TernAPI (ternary diagrams assessment programming interface) software package for ternary phase diagrams calculation by the convex hull method has been developed. Its reliability and efficiency have been proved on a large set of systems of different kind: organic liquids and fluids mixtures, water solutions, salts, oxides, metallic alloys. A remarkable advantage of TemAPI is a stable work in the case of isolated miscibility gaps ("islands") described by a uniform Gibbs energy surface equation. It also contains several improvements of phase diagram calculation algorithm, a new module for x-T diagrams polythermal sections calculation and possibility of optimization of thermodynamic models parameters. NRTL model parameters for the acetic acid N,N-dimethylformamide-cyclohexene ternary system have been optimized in this work The specialized language based on Ruby and YAML is used for the description of thermodynamic models of phases. (C) 2014 Elsevier B.V. All rights reserved.