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K-Michelson: A Michelson Semantics


K-Michelson is:

  • a formal, executable, and human-readable semantics of the Michelson blockchain programming language using the K framework;

  • a unit test framework for Michelson programs that allows testing program behavior at a finer granularity than contract invocation;

  • a formal verification framework for Michelson programs using a slight extension of Michelson as an assertion language.


  • Serve as a human-readable and executable reference document specifying how Michelson programs should operate.

  • Provide tools for testing and verifying Michelson programs operate as designed.


  • Provide a complete formal model of the Tezos blockchain. In particular, we do not model things like: networking and peer-to-peer communication, block baking or validation, transaction pools, protocol amendment, etc.

  • Replace existing Tezos CLI tools. Developers should still use tezos-client for interfacing with Tezos nodes, tezos-node for running your own nodes, etc.

Getting Started

See for installation instructions.

See for usage instructions.

Project Structure

The project has a very simple layout. Source files live at the project root.

  • specifies the syntax of Michelson and other input data

  • specifies common infrastructure used in the type checker and the core semantics

  • contains a rudimentary type-checker for Michelson

  • specifies:

    • the configuration (state representation) of Michelson programs (module MICHELSON-CONFIG)
    • the core semantic rules of Michelson as well as semantic extensions to support unit testing (module MICHELSON)
  • is a compatability layer between K-Michelson and the Tezos Reference client used for cross-validation testing

Other directories include:

  • /ext - Git submodules for our direct dependencies
  • /hooks - C++ definitions which implement some low-level operations
  • /lib - scripts used by the test harness
  • /media - source code for presentations about K-Michelson
  • /tests - source code for all tests

See the tests README for more information on test formats and organization.