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Circle SDK & Adapters Reference

Comprehensive setup references for developers integrating Circle App Kit, Unified Balance Kit, and Developer-Controlled Wallets.

1. Circle App Kit (`@circle-fin/app-kit`)

The primary entry point. Integrates swaps, sends, and bridges. Setup does not require an API kit key for standard bridge operations.

import { AppKit } from '@circle-fin/app-kit';
import { createViemAdapterFromProvider } from '@circle-fin/adapter-viem-v2';

// 1. Initialize core App Kit client
export const appKit = new AppKit();

// 2. Wrap connected Web3 provider with Viem adapter
export async function getViemAdapter(provider: any) {
  return createViemAdapterFromProvider({
    provider,
    capabilities: {
      addressContext: 'user-controlled',
      supportedChains: ['Ethereum_Sepolia', 'Base_Sepolia', 'Arc_Testnet'],
    },
  });
}

2. Unified Balance Kit

Allows checking stablecoin balances across multiple chains simultaneously. It aggregates confirmed and pending balances natively.

// Request aggregated USDC positions
const balances = await appKit.unifiedBalance.getBalances({
  token: 'USDC',
  sources: {
    address: '0x32A78... (EOA Address)',
    chains: ['Ethereum_Sepolia', 'Base_Sepolia', 'Arc_Testnet']
  },
  includePending: true,
  networkType: 'testnet'
});

console.log("Total aggregated balance:", balances.totalConfirmedBalance);

3. Swap Kit (`@circle-fin/swap-kit`)

Used server-side to calculate rate estimations and execute stablecoin swaps. Requires a backend API key.

import { SwapKit } from '@circle-fin/swap-kit';

const swapKit = new SwapKit({
  apiKey: process.env.CIRCLE_API_KEY,
  kitKey: process.env.CIRCLE_KIT_KEY
});

// Fetch estimation
const rate = await swapKit.estimateSwap({
  chain: 'Arc_Testnet',
  tokenIn: 'USDC',
  tokenOut: 'EURC',
  amountIn: '10.00'
});

// Execute transaction
const swapTx = await swapKit.swap({
  chain: 'Arc_Testnet',
  tokenIn: 'USDC',
  tokenOut: 'EURC',
  amountIn: '10.00',
  slippageBps: 100, // 1%
  recipientAddress: '0xClientAddress...'
});

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