Paymaster: The secret to making dApps feel like Web2

Introduction

Imagine a world where gas fees no longer hinder smooth and frictionless transactions. With Paymaster, we've brought this vision to life by allowing users to pay their gas fees using various tokens, eliminating the need to hold ETH or STRK just to cover transaction costs.

Whether you hold stablecoins, major tokens, or other assets, you can now transact freely, focusing entirely on using the dApp to its full potential without the hassle of gas management.

In this blog, we’ll explore Paymaster’s core functionalities, its benefits, and how you can integrate it into your Starknet dApp for a seamless user experience.

What is Paymaster? 🏦

Paymaster is an innovative solution that enables gasless transactions and flexible gas payments. Instead of requiring users to hold ETH or STRK for transaction fees, Paymaster allows dApps to either sponsor gas fees or let users pay using any supported token.

How Does Paymaster Work?

Sponsor Gas Fees: The dApp covers the user's gas costs, creating a frictionless onboarding experience.
Flexible Token Payments: Users can pay gas fees with any token they hold, not just ETH or STRK.
Meta-Transactions: Transactions can be executed on behalf of users, making interactions smoother.

Benefits of Paymaster:

✅ Frictionless UX – No need for users to manage gas tokens.

✅ Onboarding Simplification – New users can interact with dApps without holding ETH.

✅ Gas Payments in Any Token – Users can pay gas fees with stablecoins or any supported token.

✅ Improved dApp Adoption – Lower barriers encourage more interaction.

Use Case Example: Imagine a DeFi platform where users can swap tokens without worrying about ETH for gas fees. Paymaster makes this possible!

or…

POAPs! You can sponsor user’s gas fees to mint NFTs for free! Now, if that is not onboarding your grandma onchain, idk what is 🤔

AVNU’s Paymaster on Starknet 🛠️

Architecture Overview

User chooses a gas token: Instead of ETH, users select USDC, USDT, or another supported asset.
Signature Approval: Users sign a transaction without needing ETH.
API Calls: The dApp makes calls to fetch gas prices, generate typed data, and execute transactions.
Transaction Execution: The Paymaster service handles the rest, ensuring smooth blockchain execution.

Before diving into AVNU’s Gasless SDK, let's first understand why we need Paymaster and whether there are alternative solutions.

The Problem with Traditional Gas Fees

On Ethereum and Starknet, users must hold ETH (or STRK) to pay for transaction fees. This creates several friction points:

New users must acquire ETH/STRK before using a dApp.
Managing multiple tokens for gas and transactions adds complexity.
Due to gas fee requirements, DeFi, gaming, and consumer applications struggle with adoption

Are There Alternative Solutions?

There are a few other solutions available:
- Meta-transactions (Users sign messages, relayers execute the transaction, covering gas fees.)
- Third-party sponsorship services (Protocols or projects cover gas fees for new users.)
- Layer 2 scaling solutions reduce fees but still require ETH/STRK.

Among these, AVNU’s Paymaster offers a flexible and developer-friendly approach, allowing both sponsorship and token-based gas payments.

Gasless vs Gas-Free: Understanding the Difference

Gas-Free Transactions 🔥

Gas-Free means no fees for the user or dApp—transactions are executed without any cost. This typically requires a sponsor (like a project or protocol) covering all gas fees.

Gasless Transactions 💨

Gasless means the user doesn’t need ETH for gas but still pays fees using another token. This eliminates the need to manage ETH, making transactions smoother while keeping a decentralized cost structure.

Do You Need an API Key for Paymaster? 🔑

When is an API Key Required?

An API key is required in the following cases:

Sponsoring transactions – If a dApp wants to cover the gas fees on behalf of users, it must authenticate via an API key.
Using advanced Paymaster features, such as rewards-based gas sponsorship.
Building and executing typed data via the API – Required for sponsored transactions.

When is an API Key Not Required?

An API key is NOT required when:

The user is paying gas fees themselves using supported tokens (e.g., USDC, USDT, etc.).
Checking account compatibility with the gasless service.
Fetching gas token prices for display in the UI.

🏗️ Implementing AVNU’s Paymaster in Your Starknet dApp

Setting Up a Basic Starknet Project

Before jumping into AVNU’s Gasless SDK, let's first set up a basic Starknet project. This will help you understand how Paymaster integrates into a real-world dApp.

Step 1: Creating a New Starknet Project

Start by setting up a new JavaScript/TypeScript project for Starknet development.

mkdir starknet-gasless-dapp && cd starknet-gasless-dapp
npm init -y # or yarn init -y

Step 2: Installing Required Dependencies

yarn add starknet dotenv @avnu/gasless-sdk axios

Step 3: Setting Up a .env File for API Keys

Create a .env file to securely store your API keys:

touch .env

Inside .env, add:

PAYMASTER_API_KEY=your-api-key-here

Step 4: Setting Up a Basic Starknet Account & Contract Call

import { Provider, Account, Contract } from "starknet";
import dotenv from "dotenv";
dotenv.config();

const provider = new Provider({ rpc: "https://starknet.api.avnu.fi" });
const account = new Account(provider, "YOUR_ACCOUNT_ADDRESS", "YOUR_PRIVATE_KEY");

async function callContract() {
    const contract = new Contract("CONTRACT_ADDRESS", ABI, account);
    const result = await contract.call("functionName", [param1, param2]);
    console.log("Result:", result);
}

callContract();

At this point, we have set up a basic Starknet project that interacts with a contract. However, this setup still requires ETH/STRK for gas fees—this is where AVNU’s Gasless SDK comes in.

Using the Gasless SDK Without an API Key

If the user is paying gas fees in an alternative token, we can proceed without an API key.

Checking Gasless Compatibility

import { fetchAccountCompatibility } from '@avnu/gasless-sdk';

async function checkCompatibility(accountAddress) {
    const compatibility = await fetchAccountCompatibility(accountAddress);
    console.log("Gasless Compatible:", compatibility.isCompatible);
}

Fetching Gas Token Prices

import { fetchGasTokenPrices } from '@avnu/gasless-sdk';

async function getGasPrices() {
    const prices = await fetchGasTokenPrices();
    console.log("Gas Token Prices:", prices);
}

Executing a Gasless Transaction (User Pays with a Supported Token)

import { executeCalls } from '@avnu/gasless-sdk';

async function executeGasless(account, calls) {
    const response = await executeCalls(account, calls, {
        gasTokenAddress: "USDC", // User pays gas in USDC
        maxGasTokenAmount: BigInt(1000000000),
    });
    console.log("Transaction Hash:", response.transactionHash);
}

Using the Gasless SDK With an API Key (Sponsored Transactions) 🔑

If the dApp wants to sponsor gas fees, we need to use an API key. Contact AVNU to get your own API key.

Fetching Gasless Service Status

import axios from 'axios';
import dotenv from 'dotenv';
dotenv.config();

async function checkGaslessStatus() {
    const response = await axios.get('https://starknet.api.avnu.fi/paymaster/v1/status');
    console.log("Gasless Service Status:", response.data);
}

Building Typed Data for Sponsored Transactions

async function buildTypedData(userAddress, calls) {
    const response = await axios.post('https://starknet.api.avnu.fi/paymaster/v1/build-typed-data', {
        userAddress,
        gasTokenAddress: null, // Sponsored gas
        maxGasTokenAmount: null, // Sponsored gas
        calls,
    }, {
        headers: { 'api-key': process.env.PAYMASTER_API_KEY },
    });
    console.log("Typed Data:", response.data);
}

Executing Sponsored Transactions

async function executeSponsoredTransaction(userAddress, typedData, signature) {
    const response = await axios.post('https://starknet.api.avnu.fi/paymaster/v1/execute', {
        userAddress,
        typedData,
        signature,
    }, {
        headers: { 'api-key': process.env.PAYMASTER_API_KEY },
    });
    console.log("Sponsored Transaction Hash:", response.data.transactionHash);
}

📚 Additional Resources

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Paymaster: The Secret to Making dApps Feel Like Web2