txm is a command‑line utility (written for Node.js) that validates code examples embedded in Markdown documentation. By placing special `<!-- !test … -->` HTML‑comment annotations before fenced code blocks, developers can specify the program to run, its input, expected output or error, and other test expectations; txm executes the commands in parallel, reports results in TAP format, and highlights mismatches with clear diagnostics. It is aimed at authors of technical docs, libraries, or tutorials who want to ensure that the examples they publish stay correct across any language or toolchain.