SynthetixJs library

CircleCI npm version

The Synthetix-JS Library provides a simple pre-packaged API to communicate with the Synthetix payment engine on ethereum. You can use it to build your own dApp that needs to work with payments using a stablecoin.

This is particularly useful for hackathon teams to quickly npm install synthetix-js and have stable payments integrated into their dApp in just a few minutes.

Under the hood, SynthetixJs uses ethers.js library and its concept of providers and transaction signers.

The two main packages to do stable payments with are:

  • StablePayments - for transfer() and payment related functions like transfer()
  • Util - a bunch of handy utility functions for number handling and gas estimation

Some other packages for hacking with:

  • IsssuanceController - for Token swapper/exchange functions such as ETH > HAV & ETH > nUSD
  • Mintr - if you want to build a dApp for minting and burning stablecoins.

What can I build on the Synthetix payment engine?

Anything you can think of with programmable money. We provide the stability-as-a-service and fx (foreign exchange).

We’ve come up with some thought starters for dApps you could create by integrating Synthetix's stable payments into your projects.

  • Crypto Games - lottery, poker, fomoSUSD, nUSDCrash for kicks.
  • Crypto Ecommerce
  • Crypto Loans
  • Crypto Insurance
  • Crypto Payroll
  • Crypto Global Remittance

Install via npm

npm install synthetix-js

Example for getting the total nUSD stablecoin in circulation

const { SynthetixJs } = require('synthetix-js');
const snxjs = new SynthetixJs(); //uses default ContractSettings - ethers.js default provider, mainnet
(async function() {
  const totalSUSD = await snxjs.sUSD.totalSupply();
  const totalSUSDSupply = snxjs.utils.formatEther(totalSUSD);
  console.log('sUSDTotalSupply', totalSUSDSupply);

Default settings don't use any signer. That means that constants can be viewed from the contract but executing a transaction will fail. To execute transactions, set up signer.

4 signers are included in the library - Metamask (compatible with Dapp browsers), Trezor, Ledger and PrivateKey. Custom ethers.js compatible signers can be used too.

Example using a metamask signer

const { SynthetixJs } = require('synthetix-js');
const metaMaskSigner = new SynthetixJs.signers.Metamask();
const snxjs = new SynthetixJs({ signer: metaMaskSigner }); //uses Metamask signer and default provider on mainnet

Example converting ETH to USD pegged stablecoin nUSD

Obtain test ETH from a faucet

const txObj = await snxjs.IssuanceController.exchangeEtherForSynths({
  value: snxjs.util.parseEther('0.123'),

Example of making a stablecoin payment

//Transfer stablecoins to any ethereum address, wallet or smart contract
const txObj = await snxjs.StablePayments.transfer(

Example of minting stablecoin(nUSD) with private key signer

const { SynthetixJs } = require('synthetix-js');
//parameters: default provider, default networkId, private key as a string
const signer = new SynthetixJs.signers.PrivateKey(
const snxjs = new SynthetixJs({ signer });
const sUSD = snxjs.utils.toUtf8Bytes('sUSD');

async function run() {
  const totalSupply = await snxjs.Synthetix.totalSupply();
  const snxTotalSupply = snxjs.utils.formatEther(totalSupply);
  console.log('snxTotalSupply', snxTotalSupply);

  //issue 100 synths (will throw if insufficient funds for gas)
  try {
    const txObj = await snxjs.Synthetix.issueSynths(sUSD, snxjs.util.parseEther('100')); //execute transaction (requires gas)
    console.log('transaction hash', txObj.hash);
  } catch (e) {


See /__tests__ folder for more examples.

More Info

To understand the Synthetix payments engine see more at

Got any questions?

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