This is a small update on the things we have been working on and what we would like to achieve until the middle of the year.


The current focus for Act is the 0.1 release, and we are almost there. This will be Act’s first release including:

  • Support to value types, pre and post conditions, contract invariants, storage updates.
  • SMT backend to prove contract invariants and post conditions.
    • Inductive proofs or
    • Pretty printed counterexamples.
  • hevm integration to prove that the bytecode is consistent with the storage updates.
  • Many bug fixes.

After 0.1, we would like to extend the language to express loop invariants and calls to untrusted code.


We have optimized hevm for working with safe arithmetic on the bytecode level by using the techniques from this paper.

Two new hevm cheat codes useful for fuzz testing functionality involving ecrecover have been added: sign and addr. Cheat codes can now also be called with symbolic arguments, making them available for use in formal verification.

Through further generalizations, hevm now admits symbolic constructor arguments as well.

We have improved documentation to make hevm more accessible, and we are now working on a static binary for hevm which might ease some dependency issues and improve usability. We also intend to add RPC support, support for symbolic dynamic types, and synchronize loop invariants and calls to untrusted code with Act. But first, we need to implement Berlin into the hevm codebase.


The SMTChecker has become more powerful and stable over the last months, but it still lacks many usability features. We have recently added compiler options that allow the user to fine tune the model checker, including choosing the formal engine, verification targets and setting a timeout per query. The out of bounds verification target was added, reporting invalid index accesses. Counterexamples improved a lot, now reporting internal and synthesized reentrant calls, as well as concrete values for local variables. We also wrote a brand new tutorial for new users of the SMTChecker!

We want to continue improving usability in the future, reporting contract and loop invariants to the user, and creating a trusted mode for external calls to aid testing.