fee-abstraction

name	fee-abstraction
description	Pay gas fees with ERC-20 tokens on Celo. Covers supported tokens, implementation, and wallet compatibility.
license	Apache-2.0
metadata	{"author":"celo-org","version":"1.0.0"}

Fee Abstraction on Celo

This skill covers Celo's native fee abstraction feature that allows gas fees to be paid in ERC-20 tokens.

When to Use

• Paying gas fees with stablecoins (USDC, USDT, cUSD)
• Building user-friendly dApps where users don't need CELO
• MiniPay integrations
• Any Celo transaction where users prefer stablecoin gas

Overview

Celo's native fee abstraction allows gas fees to be paid in ERC-20 tokens without Account Abstraction, Paymasters, or Relay Services. Wallets simply add a feeCurrency field to transaction objects.

Source: https://docs.celo.org/developer/fee-currency

Supported Fee Currencies

Mainnet (Chain ID: 42220)

Token	Token Address	Adapter Address	Use in feeCurrency
USDC	0xcebA9300f2b948710d2653dD7B07f33A8B32118C	0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B	Adapter
USDT	0x48065fbbe25f71c9282ddf5e1cd6d6a887483d5e	0x0e2a3e05bc9a16f5292a6170456a710cb89c6f72	Adapter
cUSD	0x765DE816845861e75A25fCA122bb6898B8B1282a	-	Token
cEUR	0xD8763CBa276a3738E6DE85b4b3bF5FDed6D6cA73	-	Token
cREAL	0xe8537a3d056DA446677B9E9d6c5dB704EaAb4787	-	Token

Celo Sepolia Testnet (Chain ID: 11142220)

Token	Token Address	Adapter Address	Use in feeCurrency
USDC	0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B	0x4822e58de6f5e485eF90df51C41CE01721331dC0	Adapter

Important: Use adapter addresses for 6-decimal tokens (USDC, USDT). Use token addresses directly for 18-decimal tokens (cUSD, cEUR, cREAL).

Wallet Support

Wallet	Fee Abstraction Support	Notes
MiniPay	Full	Native support, recommended for mobile
Valora	Full	Native Celo wallet
MetaMask	No	Uses Ethereum tx format without feeCurrency field
Coinbase Wallet	No	Standard EVM format
Other EVM Wallets	No	Require custom dApp implementation

MetaMask and standard EVM wallets don't support fee abstraction because they use Ethereum-compatible transaction formats that don't include the feeCurrency field.

Library Support

Library	feeCurrency Support
viem	Supported
ethers.js	Not supported
web3.js	Not supported

viem is required for fee abstraction in dApps.

Basic Implementation

Send Transaction with Fee Currency

import { createWalletClient, custom, parseEther } from "viem";
import { celo } from "viem/chains";

// Use adapter address for USDC (6 decimals)
const USDC_ADAPTER = "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B";

const walletClient = createWalletClient({
  chain: celo,
  transport: custom(window.ethereum),
});

const [address] = await walletClient.getAddresses();

const hash = await walletClient.sendTransaction({
  account: address,
  to: "0xRecipientAddress",
  value: parseEther("0.01"),
  feeCurrency: USDC_ADAPTER, // Pay gas in USDC
});

console.log("Transaction hash:", hash);

Estimate Gas Price in Fee Currency

import { createPublicClient, http } from "viem";
import { celo } from "viem/chains";

const USDC_ADAPTER = "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B";

const publicClient = createPublicClient({
  chain: celo,
  transport: http("https://forno.celo.org"),
});

// Get gas price in USDC
const priceHex = await publicClient.request({
  method: "eth_gasPrice",
  params: [USDC_ADAPTER],
});

const gasPrice = BigInt(priceHex);
console.log("Gas price in USDC:", gasPrice);

Serialize Transaction (CIP-64)

import { serializeTransaction } from "viem/celo";
import { parseGwei, parseEther } from "viem";

const USDC_ADAPTER = "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B";

const serialized = serializeTransaction({
  chainId: 42220,
  gas: 21000n,
  feeCurrency: USDC_ADAPTER,
  maxFeePerGas: parseGwei("20"),
  maxPriorityFeePerGas: parseGwei("2"),
  nonce: 1,
  to: "0xRecipientAddress",
  value: parseEther("0.01"),
});

Key Concepts

Transaction Type

Fee currency transactions use CIP-64 type 0x7b (123 decimal). This is a Celo-specific transaction type.

Gas Overhead

Non-CELO fee currencies add approximately 50,000 gas overhead for the currency conversion.

Adapters vs Token Addresses

• 6-decimal tokens (USDC, USDT): Must use adapter address
• 18-decimal tokens (cUSD, cEUR, cREAL): Use token address directly

Adapters normalize decimals since Celo's gas calculations use 18 decimals internally.

Querying Available Currencies

Using celocli:

celocli network:whitelist --node https://forno.celo.org

Using FeeCurrencyDirectory contract:

import { createPublicClient, http } from "viem";
import { celo } from "viem/chains";

const FEE_CURRENCY_DIRECTORY = "0x9212Fb72ae65367A7c887eC4Ad9bE310BAC611BF";

const publicClient = createPublicClient({
  chain: celo,
  transport: http("https://forno.celo.org"),
});

const currencies = await publicClient.readContract({
  address: FEE_CURRENCY_DIRECTORY,
  abi: [{
    name: "getCurrencies",
    type: "function",
    stateMutability: "view",
    inputs: [],
    outputs: [{ type: "address[]" }],
  }],
  functionName: "getCurrencies",
});

console.log("Allowed fee currencies:", currencies);

Limitations

1. Wallet Dependency: Only works with Celo-native wallets (MiniPay, Valora) or custom dApp implementations
2. Library Dependency: Requires viem (ethers.js/web3.js don't support feeCurrency)
3. Gas Overhead: ~50k additional gas for non-CELO currencies
4. Balance Requirements: User must have sufficient balance in the chosen fee currency

Advanced: Custom Fee Currency Selector UI

Build a UI that lets users choose their gas payment token:

import { useState } from "react";
import { useAccount, useBalance } from "wagmi";
import { celo } from "viem/chains";

const FEE_CURRENCIES = [
  { symbol: "CELO", address: null, adapter: null },
  {
    symbol: "USDC",
    address: "0xcebA9300f2b948710d2653dD7B07f33A8B32118C",
    adapter: "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B",
  },
  {
    symbol: "USDT",
    address: "0x48065fbbe25f71c9282ddf5e1cd6d6a887483d5e",
    adapter: "0x0e2a3e05bc9a16f5292a6170456a710cb89c6f72",
  },
  {
    symbol: "cUSD",
    address: "0x765DE816845861e75A25fCA122bb6898B8B1282a",
    adapter: null,
  },
];

interface FeeCurrency {
  symbol: string;
  address: string | null;
  adapter: string | null;
}

function FeeCurrencySelector({
  onSelect,
}: {
  onSelect: (currency: FeeCurrency) => void;
}) {
  const { address } = useAccount();
  const [selected, setSelected] = useState(0);

  const handleChange = (index: number) => {
    setSelected(index);
    onSelect(FEE_CURRENCIES[index]);
  };

  return (
    <div>
      <label>Pay gas with:</label>
      <select
        value={selected}
        onChange={(e) => handleChange(Number(e.target.value))}
      >
        {FEE_CURRENCIES.map((currency, i) => (
          <option key={currency.symbol} value={i}>
            {currency.symbol}
          </option>
        ))}
      </select>
    </div>
  );
}

// Usage in transaction
function useFeeCurrencyTransaction() {
  const [feeCurrency, setFeeCurrency] = useState<FeeCurrency>(FEE_CURRENCIES[0]);

  const getFeeCurrencyAddress = () => {
    if (!feeCurrency.address) return undefined; // CELO native
    return feeCurrency.adapter || feeCurrency.address;
  };

  return { feeCurrency, setFeeCurrency, getFeeCurrencyAddress };
}

Advanced: Server-Side Transaction Building

Build fee currency transactions server-side for gasless or sponsored transactions:

import { createWalletClient, http, parseEther } from "viem";
import { privateKeyToAccount } from "viem/accounts";
import { celo } from "viem/chains";

const USDC_ADAPTER = "0x2F25deB3848C207fc8E0c34035B3Ba7fC157602B";

async function buildSponsoredTransaction(
  recipientAddress: `0x${string}`,
  amount: bigint
) {
  // Sponsor account pays gas in USDC
  const sponsorAccount = privateKeyToAccount(
    process.env.SPONSOR_PRIVATE_KEY as `0x${string}`
  );

  const walletClient = createWalletClient({
    account: sponsorAccount,
    chain: celo,
    transport: http("https://forno.celo.org"),
  });

  const hash = await walletClient.sendTransaction({
    to: recipientAddress,
    value: amount,
    feeCurrency: USDC_ADAPTER,
  });

  return hash;
}

// Example: sponsor a user's transaction
async function sponsorUserTransfer() {
  const hash = await buildSponsoredTransaction(
    "0xUserAddress",
    parseEther("1")
  );
  console.log("Sponsored transaction:", hash);
}

Additional Resources

• fee-currencies.md - Complete token addresses and adapters
• wallet-support.md - Detailed wallet compatibility guide