ts-pnp is a low-level package that adds transparent support for Plug'n'Play to TypeScript by implementing the `resolveModuleName` hook from `CompilerHost`. It's designed for developers writing TypeScript compiler hosts who need to resolve module names in a way that works seamlessly whether or not the application is running under Plug'n'Play. For most users who just want to write TypeScript, the project recommends using higher-level integrations like `pnp-webpack-plugin` instead.