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POSTED 08 Mar 2019 19:18

Smart Contract Utilities with ZeppelinOS: Linking, Publishing, and Vouching


A feature of ZeppelinOS is the ability to link to EVM packages that are already deployed. In this tutorial, we will learn how to link to these packages and publish our own!


  • Node.js
  • An understanding of Solidity the programming language for smart contracts.
  • Truffle, a development framework for Ethereum to test and deploy smart contracts.
  • Ganache, a personal blockchain installed to test and run our smart contracts.


After installing Node.js we are now ready to install ZeppelinOS. Using the terminal do the following:

Note: For Windows users, I recommend Powershell over Command Prompt.

npm install -g zos

That's it! We installed ZeppelinOS.

Note: zos --help gives you a full list of all ZeppelinOS commands should you require them.

Creating our project

In the directory of your choice, create your project and then change to that directory:

mkdir first-project
cd first-project

Now we're going to create our project.json file to store the relevant data for the project. You will see a dialogue of properties to fill in. Fill them in if you wish or press enter to leave as the default.

npm init

To initialize as a ZeppelinOS project run the following:

zos init first-project

This command initializes a Truffle config file, two empty folders called contracts and migrations, and a zos.json file which has more information about the project in relation to ZeppelinOS.

The last step is to download the ZeppelinOS project library.

Note: You have to install this library with every project, you can't use it from project to project.

npm install zos-lib --save

Creating a Contract

Open your project in a text editor of your choice (I'm using Atom) and create a new file called MyToken.sol under the contracts folder.

pragma solidity ^0.5.0;

import "openzeppelin-eth/contracts/token/ERC20/ERC20.sol";
import "openzeppelin-eth/contracts/token/ERC20/ERC20Detailed.sol";

contract MyToken {
  ERC20Detailed private _token;

  function initialize(ERC20Detailed token) external  {
    _token = token;

openzeppelin-eth is an EVM package that is already deployed and it contains the same contracts that OpenZeppelin does. The difference between the two is that OpenZeppelin is not deployed to the network.

Now let's link our contract to the package:

zos link openzeppelin-eth

Right now the openzeppelin-eth EVM package has StandaloneERC20, StandaloneERC721, TokenVesting, and PaymentSplitter contracts pre-deployed. This means that these are the only contracts you can utilize in the EVM package.

We are now linked. It's time to compile and add the contract to our project:

truffle compile

zos add MyToken

Now in a separate terminal run ganache.

ganache-cli --port 9545 --deterministic

Open your original terminal and start a new session. For the address, you can choose any of the addresses from the ganache window under the "available accounts" section. I'm using the 9th address.

zos session --network local --from ganache-address-here --expires 3600

Note: If you get a message at any point saying "A network name must be provided to execute the requested action" it means that our session expired. Run the zos session command from above and try again from where you left off.

Now push our contract to the local network.

zos push --deploy-dependencies --network local

It's time to create an instance of our contract and the package we linked using the StandaloneERC20 contract to create an instance of an ERC20 token.

zos create MyToken

zos create openzeppelin-eth/StandaloneERC20 --init initialize --args JToken,JTKN,18,100,Juliette,[],[] --network local

The arguments are as follows: name, symbol, decimal, initial supply, initial holder, minters address, and pausers address. We left the last two empty and put "Juliette" instead of an address for who owns the token. You should see output describing what you've initialized.

The last step is to use the truffle console to connect MyToken and StandalineERC20 together. Open your file and scroll down to where you see token-project/MyToken and openzeppelin-eth/StandalineERC20. The addresses listed in those sections are the ones you use in the following commands.

truffle console --network local

myToken = await'<MyToken-address>')
> undefined


After this command, there should be a lot of output detailing the transaction.

That's it! You've linked to an EVM package and deployed it on your local blockchain with the arguments we submitted above and successfully joined our StandaloneERC20 token contract with our MyToken contract.


We've seen how to deploy, upgrade, and link our smart contracts. Now it's time to learn about publishing. If you've created your own EVM package, you have the option of publishing it to the network for others to use.

Note: If you follow the steps in this section of the tutorial you publish your package to the network. If you don't want to do that, use this section as a reference.

Create your project and initialize it:

mkdir project-name
cd project-name
npm init
zos init project-name

Within the contracts folder, we create our contract/package. Once finished we use the add command:

zos add contract-name-here

Then we can push our contract to the network. We have to use a real network, not a local network for it to deploy and be available for others to use.

zos push --network {network-here}

Replace {network-here} with the network you are going to publish to.

Next, we edit the package.json file. Add the following to the bottom of the file.

"files": [

Before adding this code, make sure that you change the second last bracket to have a comma after it. Your file should look something like this:

  "name": "",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \\"Error: no test specified\\" && exit 1"
  "author": "",
  "license": "ISC",
  "dependencies": {
    "openzeppelin-eth": "^2.1.3",
    "zos-lib": "^2.1.2"
  "files": [

If you have a"network id".json file you can remove it now because it was specific for your local test network.

When you're ready:

npm login

You'll see a prompt to fill in your credentials to create an NPM account such as username, password and email address. Once you have an account. The last step is to publish your package to npm.

npm publish

If any developers ever want to link to your package, they use the following commands:

zos link your-project-name

That's it! It's easy to publish an EVM package and it's even easier to link to one!


Vouching is useful to ensure the authenticity of a package. Anyone can create an EVM package but not all packages are useful or reliable. Vouching provides a way for the user to measure the quality of code. Right now vouching is in its beta stage and the following contract controls it. The ZEP token is an ERC20 token that will be used to vouch in this process. This is the next feature to be released.

Next Steps