gcode-preview is a TypeScript library for rendering 3D-print toolpath previews from G-code files in web applications. It parses G-code command streams, interprets motion and extrusion commands, organizes the resulting paths into layers and tool segments, and renders them as either flat colored lines or volumetric tubes using Three.js. The library is structured as a pipeline of independently testable modules: a line-oriented parser, a stateful interpreter, a job/path model, and a Three.js scene manager. A Vue 3 demo application is included to exercise the library, but the repository is fundamentally a reusable npm package with ESM and UMD builds, unit tests, Firebase-hosted demo infrastructure, and publishing CI.