Massa SMART-CONTRACTS Documentation


A smart contract is a transaction protocol used to be sure that an operation, involving different stakeholders, is executed as expected.

Having trust between stakeholders is not necessary, as long as each participant is trusting the transaction protocol.


full documentacion : Introduction — Massa documentation

By adding a programmable mechanism to the blockchain, we get such a protocol as long as the program has the following characteristics:

  • Immutability
  • Determinism
  • Audit


Smart contract is not about replacing paper contract with electronic one, but replacing the Law with the transaction protocol. By doing so you’re also replacing trust in justice by trust in the blockchain.

In the following, and in the crypto ecosystem, we talk about smart contracts only to refer to a program that can be executed on a blockchain.

Nevertheless, it’s important to keep in mind that the transaction protocol exists and is valued only thanks to the entanglement of the program in the blockchain and its guarantees.

Technical choices

For all the reasons listed above and for performance, Massa chose a program in WebAssembly.

For the sake of accessibility, Massa decided to use AssemblyScript as programming language to compile the expected logic into bytecode.

Finally, at node level, the byte of a program is executed by Wasmer.

The following schema recap graphically all this:


Getting started

In this section you will learn how to compile your first Massa smart contract.

Setting up a new project

Wait, I know npm. Just give me the commands!
npm init
npm install --global yarn npx
npm install --save-dev @as-pect/cli massa-sc-std
npx asinit .
npx asp --init
OK, but I would like to use docker. Can you help me?

docker run -it --user $(id -u):$(id -g) -v $PWD:/app -v $PWD/.npm:/.npm -v $PWD/.config:/.config -w /app node:17.7-alpine npm init
docker run --user $(id -u):$(id -g) -v $PWD:/app -v $PWD/.npm:/.npm -v $PWD/.config:/.config -w /app node:17.7-alpine npm install --save-dev @as-pect/cli
docker run -it --user $(id -u):$(id -g) -v $PWD:/app -v $PWD/.npm:/.npm -v $PWD/.config:/.config -w /app node:17.7-alpinenpx asinit .
docker run --user $(id -u):$(id -g) -v $PWD:/app -v $PWD/.npm:/.npm -v $PWD/.config:/.config -w /app node:17.7-alpine npx asp --init

Make sure you have a recent version of Node.js and npm. Update or install them if needed. Create or go to the directory where you want to set up your project and run:

npm init
npm install --global yarn npx

Don’t bother with the different question, you can change all that by editing the package.json file.


You can add the parameter –yes to automatically set the default values.

See also  People at the heart of #blockchain

Now that the npm project is created, install the as-pect and massa-sc-std dependencies by executing the following command:

npm install --save-dev @as-pect/cli massa-sc-std massa-sc-scripts

You have now installed AssemblyScript and as-pect modules. The first one will be used to generate bytecode from AssemblyScript code and the second one will let you perform unit tests.


  • Massa smart contract module (massa-sc-std) contains the API you need to use to interact with the external world of the smart contract (the node, the ledger…).
  • Installing directly as-pect will automatically install the compatible version of AssemblyScript.
  • All dependencies should be installed as dev dependencies as no module will be exported on this project.

Now that AssemblyScript and as-pect dependencies are installed, you can finish setting up your project by running:

npx asinit .
npx asp --init

Congratulations! Now you have a fully set up project and you are ready to add some code.


A few words on project folders:

  • assembly is where the code goes;
  • assembly/__test__/ store the unit tests;
  • build will contain the compiled smart contracts.

Create your first smart contract

Since the beginning of mankind, humans explain how to use a program, a new language, a service by implementing a Hello world!.

Your first smart contract will be no exception!


I’m told that it has nothing to do with the beginning of mankind but Brian Kernighan used it for the first time in a tutorial introduction to the language B published in 1972.

Create and open a new file called helloworld.ts in assembly directory at the root of your project. In this file, write or copy/paste the following code:

import { print } from "massa-sc-std";

export function main(_args: string): void {
    print("Hello world!");

Don’t forget to save the file. Before starting compilation, just a few words to describe what you just wrote or pasted:

  • line 1: print function is imported from Massa API (massa-sc-std). This function will write to stdout the string given as argument.
  • line 3: main function is exported. This means that the main function will be callable from the outside of the WebAssembly module (more about that later).
  • line 4: print function is called with “Hello world!”. Brian, we are thinking of you!

Now that everything is in place, we can start the compilation step by running the following command:

npx massa-sc-scripts build-sc assembly/helloworld.ts

Congratulations! You have generated your first smart contract: the helloworld.wasm file in build directory.


If due to bad luck you have an error at compilation time:

  • check that you properly followed all the steps,
  • do a couple a internet research,
  • look for any similare issue (open or closed) in this project.

If you find nothing, feel free to contact us on Discord or directly open an issue here.


Execute your smart contract on a node

To execute the smart contract you will need:

  • A running node with a log level set to DEBUG.
  • A client configured with an address having coins.
  • A smart contract compiled in WebAssembly (see previous step).

Let’s go!

Running a node in debug mode

Make sure that you have the last version of the Massa node. If not, install it.

Once the node is installed and before running it, set your log level to DEBUG:

  • open massa-node/base_config/config.toml file with your preferred editor;
  • set the log level to 3.


Your file should look like the following:

# Logging level. High log levels might impact performance. 0: ERROR, 1: WARN, 2: INFO, 3: DEBUG, 4: TRACE
level = 3


A node configured with a verbose log level will write a lot of logs. You should restore default value as soon as this tutorial is finished.

Now that the node is properly configured to log print function output you have to run the node.

Configure the client

If you don’t have any wallet configured yet, create a new one.

If you’re using a brand new wallet, add some coins by sending your address to testnet-faucet discord channel.

If you are using an existing wallet, make sure that you have at least 1 coin on it.

In any case, keep the address of your wallet, you will use it later.

Execute the smart contract on the node

Everything is in place, we can now execute the hello world smart contract on your local node with the following command inside the client cli:

send_smart_contract <address> <path to wasm file> 100000 0 0 0


We are executing the send_smart_contract command with 6 parameters:

  • <address>: the address of your wallet kept during previous step;
  • <path to wasm file>: the full path (from the root directory to the file extension .wasm) of the hello smart contract generated in the previous chapter.
  • 100000: the maximum amount of gas that the execution of your smart-contract is allowed to use.
  • Three 0 parameters that can be safely ignored by now. If you want more info on them, use the command help send_smart_contract.

If everything went fine, the following prompted message should be prompted:

Sent operation IDs:
<id with numbers and letters>

In that case, return to the node tab and have a look at the log, you should see a message like the following:

<date and time> DEBUG massa_execution_worker::interface_impl: SC print: Hello world!

Congratulations! You have just executed your first smart contract on a node !!

Don’t forget to change node’s log level to INFO (value is 2).

Store a smart contract in the blockchain

Full documentation     —-   Getting started — Massa documentation
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