Echidna

What it is

A property-based testing tool from Trail of Bits, written in Haskell. It generates call sequences from a contract ABI and keeps mutating them until a stated property fails or the run budget ends.

What it helps with

- Testing invariants such as balance limits or supply rules
- Catching failed assertions, including Foundry-style assert helpers
- Saving a corpus and using coverage to reach deeper code paths
- Shrinking a failing sequence to the shortest call path that breaks it

Who it's for

Smart contract auditors and security engineers testing contracts they own or are authorized to assess.

Worth knowing

Properties are Solidity functions whose names start with echidna_, take no arguments, and return a boolean. The default mode tests those functions, and an assertion mode checks assert statements instead.

Does it need Slither?
Yes, it uses Slither during compilation to collect contract information, and the Homebrew package installs both.

Can it test contracts on a live chain?
Yes, it can fetch deployed contract code and state from an RPC endpoint during a run.