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Halmos

Symbolic testing for EVM smart contracts

a16z's symbolic testing tool that runs Foundry-style tests with symbolic inputs to prove properties or find counterexamples.

Open sourceAGPL-3.0-only
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Homepage of Halmos
Official repository page, captured by ThreatWire.

What Halmos does

Halmos reuses tests written for Foundry but treats inputs as symbolic values. Instead of trying random inputs like a fuzzer, it explores paths with an SMT solver and either reports that an assertion holds within the explored bounds or returns a concrete counterexample.

It brings bounded formal verification into a familiar testing workflow and is developed by a16z crypto.

Key features

  • Symbolic execution of Foundry tests
  • Counterexample generation
  • Bounded verification of properties
  • Invariant testing support
  • Works on existing test suites

Licence

AGPL-3.0-only · GNU AGPL v3 · Open source

Checked by ThreatWire against the repository's licence file on 2026-10-20. GitHub detects: AGPL-3.0.

Security of Halmos itself

No published advisory found for Halmos in GitHub repository advisories. That does not mean the tool has no vulnerabilities.

Sources: GitHub repository advisories · checked 2026-10-20.

Categories and tags

Smart contract security#symbolic-testing#formal-verification#foundry#evm

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