This is a TeX-to-HTML+MathML+CSS converter class using the Javascript-based KaTeX, interpreted by one of the Javascript engines supported by ExecJS. The intended purpose is to eliminate the need for math-rendering Javascript in the client's HTML browser. Therefore the name: SsKaTeX means Server-side KaTeX. Javascript execution context initialization can be done once and then reused for formula renderings with the same general configuration. As a result, the performance is reasonable. The configuration supports arbitrary locations of the external file katex.min.js as well as custom Javascript for pre- and postprocessing. For that reason, the configuration must not be left to untrusted users.