> ## Documentation Index > Fetch the complete documentation index at: https://developers.circle.com/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}. > Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts. > Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md. > Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md. > Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers. > Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews. > Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming. > Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md. > Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors. > API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product. > Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes. > When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records. > Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md. # Grant USDC allowance to Permit2 > Use Uniswap's Permit2 contract to grant USDC allowance to the StableFX FxEscrow contract This guide shows an example of how to grant a USDC token allowance to the `Permit2` contract using a Circle Wallets developer-controlled wallet. The [`Permit2` documentation](https://docs.uniswap.org/contracts/permit2/overview) provides additional examples of how to grant this allowance. When using the [StableFX API](/stablefx/concepts/technical-guide) to deliver the funds onchain for an FX trade, you must grant an allowance to the [`Permit2` contract](https://docs.arc.io/arc/references/contract-addresses#permit2) for the token you are funding. This allows the `Permit2` contract to transfer the token from your wallet to the `FxEscrow` contract. ## Prerequisites Before you begin, ensure you have: * A [Circle Developer Console](https://console.circle.com/) account. * A [developer-controlled wallet](/wallets/dev-controlled/create-your-first-wallet) * [Node.js 18+](https://nodejs.org/) installed. * A project set up as described in the below section ### Set up your project 1. Initialize a new Node.js project and install dependencies: ```shell theme={null} npm init -y npm pkg set type=module npm install viem dotenv ``` 2. In the project root, create a `.env` file and add the following variables: ```shell theme={null} USDC_CONTRACT_ADDRESS= PERMIT2_CONTRACT_ADDRESS= APPROVAL_AMOUNT= WALLET_ADDRESS= ``` The `PERMIT2_CONTRACT_ADDRESS` is the same across all EVM blockchains (`0x000000000022D473030F116dDEE9F6B43aC78BA3`), but you should verify it with the blockchain explorer on the chain you are using. You can find the `USDC_CONTRACT_ADDRESS` on the [USDC contract address page](/stablecoins/usdc-contract-addresses). The USDC token has 6 decimals. To approve \$100 USDC, set `APPROVAL_AMOUNT` to `100000000` (100 \* 106). If you are following the Circle Wallets example, you will also need to add the following variables: ```shell theme={null} CIRCLE_WALLET_ID= CIRCLE_WALLETS_API_KEY= ENTITY_SECRET= ``` If you are not funding USDC, you need to grant allowance using the contract address of the token you are funding. 3. Create an `index.js` file. You'll add code step by step in the following sections. ### Grant a USDC token allowance to the `Permit2` contract Add the following code to your `index.js` file to grant a USDC token allowance to the `Permit2` contract using a Circle Wallets developer-controlled wallet on supported EVM blockchains. ```javascript theme={null} import { initiateDeveloperControlledWalletsClient } from "@circle-fin/developer-controlled-wallets"; import { randomUUID } from "crypto"; import dotenv from "dotenv"; dotenv.config(); /** * Approves a specified amount of USDC for the Permit2 contract using * a developer-controlled wallet managed by Circle. * * This function sends an on-chain transaction to call the ERC-20 `approve` * method on the USDC contract, allowing the Permit2 contract to spend * the specified amount on behalf of the wallet. * * @async * @function approveUSDCWithCircleWallets * @returns {Promise} The transaction response data returned by Circle's API. */ export async function approveUSDCWithCircleWallets() { const client = initiateDeveloperControlledWalletsClient({ apiKey: process.env.CIRCLE_WALLETS_API_KEY, entitySecret: process.env.ENTITY_SECRET, }); const response = await client.createContractExecutionTransaction({ walletId: process.env.CIRCLE_WALLET_ID, contractAddress: process.env.USDC_CONTRACT_ADDRESS, abiFunctionSignature: "approve(address,uint256)", abiParameters: [ process.env.PERMIT2_CONTRACT_ADDRESS, process.env.APPROVAL_AMOUNT, ], idempotencyKey: randomUUID(), fee: { type: "level", config: { feeLevel: "MEDIUM" } }, }); return response.data; } /* -------- Example usage with Circle --------- // For auth and wallet creation, see: https://developers.circle.com/interactive-quickstarts/dev-controlled-wallets const response = await approveUSDCWithCircleWallets(); console.log('Response:', response); ---------------------------------- */ ```