AMC: Towards Trustworthy and Explorable CRDT Applications with the Automerge Model Checker

Conflict-free Replicated Data Types (CRDTs) enable local-first operations and asynchronous collaboration without the need for always-on centralised services. CRDTs can have a high overhead, so implementations need to be optimised, but this optimisation can lead to bugs despite the use of test suites and fuzzing. Furthermore, using CRDTs in applications is complex, observing unexpected conflict resolution, issues synchronising documents and difficulties implementing appropriate data models. Automerge is a library, exposing a JSON CRDT, that sees users having difficulties in modelling their problems, understanding their edge cases and implementing applications correctly. We introduce the Automerge Model Checker (AMC), empowering application developers to check properties about their implementations and explore them dynamically. AMC can check a range of applications as well as being able to check properties about the core of Automerge itself, helping to make more trustworthy Automerge applications. AMC is available open-source at github.com/jeffa5/automerge-model-checker.