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The Pact Programming Language

Build Status

Pact is an open-source, Turing-incomplete smart contract language that has been purpose-built with blockchains first in mind. Pact focuses on facilitating transactional logic with the optimal mix of functionality in authorization, data management, and workflow.

Read the whitepaper:

For additional information, press, and development inquires, please refer to the Kadena website

Table Of Contents


Extensive tutorials on every facet of the Pact language may be found on Additionally, users may find example scripts in Kadena's pact-examples repository, in the examples directory, and in production as part of the Kadena Public Blockchain.


The Pact language specification, API documentation, features, motivations, and in-depth tutorial content may be found here.

Documentation is always in flux, and corrections to out of date documentation are always appreciated. Feel free to do so if you find such an error by opening an issue.


The easiest and quickest way to try Pact is in the browser, or via the Chainweaver wallet. Both environments support error and warning highlighting, as well as an in-app REPL environment for you to test out your code immediately. The Kadena docs also include a developer quickstart.

Installing Pact

Binary Distributions

Pact can be installed via binary distribution for Linux or Mac by following the instructions below:

  • Install z3.
  • Download the prebuilt binaries for either Linux or Mac, depending on your OS.
  • Once you've downloaded the binary, make sure that it is marked as executable by running chmod +x <executable-file>.
  • Put the binary somewhere in your PATH.

Once you have Pact in your path, proceed to validating your installation by trying out the repl.

Instructions for Mac Users

Using Brew

On Mac, the easiest way to install pact is with Homebrew. Make sure that Homebrew has been installed in your machine. Instructions for how to install it can be found here. Once Homebrew is installed, run the following command to install pact:

brew update
brew install kadena-io/pact/pact

If you want to install from source, see building from source

Instructions for Linux Users

Linux is supported in terms of both the binary distributions (see below) and building from source. For installing pact on Linux distributions in the Arch family, refer to this package on the AUR. Otherwise, please refer to building from source.

Building from Source


  • (Mac only) Homebrew: brew install git
  • (Linux/Mac) Installer

To get the code, you can go here. Once you have the code, we can pick a build tool.

Building with Cabal

Cabal is the preferred way to manage packages by the Haskell community. You will need a version of GHC installed on your machine to use it.

  • ghc >= 8.4 (Haskell compiler) and cabal >= 2.2 (Haskell build-tool)
    • The easiest way to get this is to install it using (Linux/Mac) ghcup and issue ghcup install 8.6.5, followed by ghcup install-cabal.
    • ghc may also be installed via brew, issuing brew install ghc and brew install cabal-install.

(You may also need to install zlib, z3, and sqlite)

To build a Pact binary:

# Only necessary if you haven't done this recently.
cabal v2-update

# Build the project.
cabal v2-build

On some systems the default build might fail with linker errors complaining about cryptonite and ed25519, try:

# configure cabal 
cabal v2-configure -f cryptonite-ed25519

# Build the project.
cabal v2-build

This will install a runnable version of Pact, which you can run via:

cabal v2-exec pact

Alternatively, cabal v2-install will install the binary to ~/.cabal/bin/, which you may need to add to your path. Then, you can call pact as-is.

Building with Stack

(stack is no longer supported)

Stack is a Haskell build tool that manages compiler and dependency versions for you. It's easy to install and use.

  • stack >= 1.9
    • (Mac only) Homebrew: brew install haskell-stack
    • (Linux/Mac) Installer

(You may also need to install zlib, z3, and sqlite)

To build a Pact binary:

stack build

This will compile a runnable version of Pact, which you can run via:

stack exec pact

Alternatively, stack install will install the binary to ~/.local/bin/, which you may need to add to your path. Then, you can call pact as-is.

Building with Nix

The fastest way to build and run Pact is to use the Nix package manager which has binary caching capabilities that allow you to download pre-built binaries for everything needed by Pact. For detailed instructions see our wiki.

When the build is finished, you can run Pact with the following command:


Verifying Installation

Test by issuing pact in a terminal or by executing your binary. Try out some commands:

$ pact
pact> (+ 1 2)
pact> (+ "hello, " "world")
"hello, world"

Supported Editors

Pact is supported by a variety of editors ranging from full-fledged IDE environments to syntax highlighting.


The Chainweaver wallet is the Kadena's wallet, offering a seamless IDE experience and wallet in one. It supports a full in-app REPL, code preview, error/warning highlighting, code deployment, key generation, and integration with existing Kadena blockchains.


An implementation of Chainweaver exists in the browser, if you do not wish to download the wallet.


For a full-fledged IDE experience, install the Atom editor along with language-pact using the atom package manager.

VS Code

The Pact language has community support for VS Code via the pact-vscode package. (


Emacs has pact-mode support via MELPA, along with flycheck-pact for on-the-fly error highlighting. Download pact-mode and (optionally) flycheck-pact by opening Emacs and issuing M-x package-list-packages, syncing MELPA, and installing by name. Then, in your init.el or .emacs, include

(use-package pact-mode
  :ensure t
  ;; optionally
  (require 'flycheck-pact))

If you've chosen to include flycheck-pact, you can start the interactive buffer and trace by calling flycheck-pact-toggle-trace and flycheck-pact-interactive-buffer.


If you are a vim user, the vim-pact plugin provides support for the pact syntax.

The Pact REST Api

Api Documentation

The REST API is documented at

Pact REST API Server

Pact features a full REST API HTTP server and SQLite database implementation, making blockchain application development painless and easy. The Pact server simulates a single-node blockchain environment, with the same API supported by the Kadena ScalableBFT blockchain.

To start the server, issue

pact --serve CONFIG


pact -s CONFIG

where CONFIG is a valid config.yaml.

Hosting static files.

The HTTP server will host any static files it finds in its working directory.

Config file format

The pact dev server (pact-serve) requires a configuration Yaml file (e.g. server.conf) to operate. The documentation for it is:

console> pact --serve --help
Config file is YAML format with the following properties:
port       - HTTP server port
persistDir - Directory for database files.
             If ommitted, runs in-memory only.
logDir     - Directory for HTTP logs
pragmas    - SQLite pragmas to use with persistence DBs
verbose    - [True|False] Provide extra logging information

Replay from disk.

When running pact-serve with persistence enabled, the server automatically replays from the database commands.sqlite in the persist dir. To prevent replay, simply delete this file before starting the server.

Related Projects

  • The pact-lang-api npm package provides a JavaScript library to aid interaction with the API.

  • The pact-todomvc is a working demonstration.


This code is distributed under the terms of the BSD3 license. See LICENSE for details.