Write symbolic Foundry tests that verify Solidity properties across all inputs within bounds.
npx skills add https://github.com/naruto11eth/cryptoskills --skill halmos-naruto11eth
Please help me install this Agent Skill. Skill: halmos Source: https://github.com/naruto11eth/cryptoskills/tree/main/skills/halmos Command: npx skills add https://github.com/naruto11eth/cryptoskills --skill halmos-naruto11eth
check_ prefixed Foundry tests where parameters become symbolic variables, constrain inputs with vm.assume, and verify properties with raw assert(). - Bounded model checking: Configure --loop and --depth bounds, solver timeouts, and storage layouts to balance verification confidence against CI runtime. - Counter-example debugging: Decode Halmos counter-examples, reproduce them as concrete Foundry tests, fix the bug, and re-verify. - Use Case: A DeFi team needs to prove a vault invariant (totalAssets >= totalShares) holds for every deposit and withdrawal. They write check_ tests, run halmos --loop 5 in CI, and get mathematical assurance within bounds without learning Certora's CVL. ## Quick Start Ask the agent to write a Halmos symbolic test that verifies your ERC-20 transfer function preserves total supply for all possible inputs.High-intent search queries and answers about installing and using this skill.
Write a Foundry test function prefixed with check_ instead of test_, and its parameters become symbolic variables covering all possible values. Constrain inputs with vm.assume, verify properties with raw assert(), then run the halmos CLI after forge build.
Foundry's fuzzer runs tests with random concrete inputs, giving statistical coverage. Halmos executes tests symbolically, reasoning about all possible inputs simultaneously within loop and depth bounds, and produces concrete counter-examples when assertions fail.
Halmos is a bounded model checker that runs locally with no API key and uses plain Solidity tests, making it suited for quick CI property checks. Certora provides unbounded formal verification but requires learning the CVL specification language and a paid API key.
Zero paths means your vm.assume constraints are contradictory, so no valid inputs exist and the property holds vacuously. Remove assumptions one at a time until the path count increases, keeping only necessary preconditions.
forge-std assertions like assertEq revert on failure, and Halmos treats reverts as valid execution paths rather than property violations. Use raw assert() for symbolic properties so Halmos checks them with the SMT solver.
Halmos only verifies properties up to the --loop and --depth bounds, so bugs beyond those bounds are missed. It also lacks fork mode, supports only a subset of Foundry cheatcodes, and can hit solver timeouts on complex non-linear arithmetic.
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