Programming languages rarely have a formally defined semantics, although it is the only way to ensure unicity in the interpretation of a language. On of the main reasons thereof is how hard it is to write a semantics, and how few applications there is. To this end, we introduce Skel, a simple language to describe programming languages' operational semantics, and Necro, an ecosystem to manipulate them, allowing among other things to generate interpreters and debuggers. Furthermore, Skel being minimal, and Necro being extensible, it is easy to add a new backend, in order to extract Skel semantics to other tools.Les langages de programmation ont rarement une sémantique définie de manière formelle. Pourtant, c'est la seule manière de garantir ...