create-formal-verification-skill

• SKILL.mdcore · 5,626 bytes

# Create a formal verification skill

A test checks the cases that someone thought to write. Formal verification checks every case in a stated scope: every order of steps in a model, every input up to a bound, or every input. This skill finds the part of the repo where that matters most, verifies one property of it, and leaves a project-local skill that lets the next agent check a change against that property. Write that skill for an agent who reads it cold, mid-change, and has never seen your work. The user must be able to trust the result and act on it without learning the verification language.

## Choose the target from the code

Answer from the codebase, and ask the user only what you cannot observe. If the user named an area or a bug, start there.

A good target is a promise the code makes, where a break harms users and tests rarely reach the case that breaks it. Choose the strongest such target in the repo, not the one that is easiest to verify.

## Let the question choose the tool

Pick the tool that answers the question at the lowest cost: a model checker, a proof assistant, an SMT-backed verifier, or another tool. Whether events can happen in a bad order usually suits a model checker over a small model of the design, and TLA+ is the default for that in any language. Whether the code itself behaves for every input, as with memory safety, overflow, or a data-structure invariant, usually suits a verifier that runs on the code. If no verifier runs on this language, say so, and test the real code with generated inputs, not a hand model of the function. A property that must hold at every size, where a bound is not enough, can need a proof. Prefer a tool that the repo's developers can install and run, and tell the user why you chose it.