# a16z/halmos

A symbolic testing tool for EVM smart contracts

Repository: https://github.com/a16z/halmos
Canonical: https://ross.abutalabs.com/products/halmos
Language: Python
License: AGPL-3.0
License Family: copyleft
Last push: 2025-08-06T19:05:39+00:00

## Health v2 (maintenance only)
Score: 50/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 35, release rhythm 41, longevity 97
- inputs: {"age_days": 1360, "days_push": 392, "days_rel": 399, "gap_med": 23.5, "n_releases_24m": 11}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1028, forks 110 (observed 2026-08-28T04:03:17.489024+00:00)

## What it is
Halmos is a symbolic testing tool for EVM smart contracts, primarily targeting Solidity projects via a Foundry frontend. It leverages existing test suites to perform formal-verification-style checks using symbolic execution and SMT solvers.

## Use cases
- symbolically test solidity smart contracts
- formally verify evm contract invariants using existing foundry tests
- find counterexamples to contract properties automatically
- check smart contract equivalence between implementations
- run formal verification on ethereum contracts from the command line

## When to choose
- you have a foundry/solidity test suite and want stronger guarantees without rewriting tests
- you want lightweight formal verification of evm contracts
- you need automated counterexample generation for contract properties

## When to avoid
- you need full formal verification of complex contracts beyond what symbolic testing can prove
- your contracts are written in languages not yet supported like vyper or huff
- you need runtime fuzzing rather than symbolic execution

## Facets
- artifact type: cli-tool
- maturity: active
- function: testing, security, developer-tools, cli
- domain: security, blockchain, developer-tools, testing
- platform: python, cli
- tags: evm, smart-contracts, solidity, formal-verification, symbolic-execution, foundry, smt-solver, linux, macos, docker

## Member repositories
- a16z/halmos (main) score 50

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:03:17.489024+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T07:07:43.844241+00:00, confidence not recorded.
  - readme: https://github.com/a16z/halmos (fetched 2026-08-28T04:03:17.489024+00:00, sha 8bb6a30bbf10)
  - registry_pypi: https://pypi.org/pypi/halmos/json (fetched 2026-08-29T13:07:52.707332+00:00, sha 024190ccda38)
- Data as of 2026-08-30T08:39:29.467469+00:00.