Echidna

Echidna is an open-source property-based fuzzer for Ethereum smart contracts, maintained by Trail of Bits. You define properties or invariants that should always hold, and Echidna generates long, coverage-guided sequences of transactions trying to violate them.

What It Does

Echidna is particularly strong at stateful testing: it drives a contract through many action sequences with different callers and inputs, reporting any sequence that breaks an invariant as a concrete, reproducible counterexample. This surfaces emergent bugs that only appear after specific orderings of calls.

Where It Fits

Fuzzing with Echidna complements static analysis (Slither) and symbolic execution (Mythril). It only tests the properties you write, so good invariants are essential.

Frequently Asked Questions

Q: What kind of bugs does Echidna find?

A: Emergent, multi-step bugs — accounting drift, broken solvency conditions, or state that violates a declared invariant after a particular sequence of calls.

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Q: Do I need to write properties for Echidna?

A: Yes. Echidna tests the invariants and properties you define, so its effectiveness depends on writing meaningful ones.