> ## 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.

# Getting started with the Contracts Node.js SDK

Use the
[Node.js SDK](https://www.npmjs.com/package/@circle-fin/smart-contract-platform)
to interact with [Contracts APIs](/api-reference/contracts/common/ping), which
allow you interact with smart contracts on the blockchain using the Developer
Services platform.

This page provides short examples of how to install and use the Contracts SDK.
For complete examples, see the [Sample Projects](/sample-projects) page. For
more information see the [Contracts documentation](/contracts).

## Prerequisites

To use the Node.js SDK, ensure you have:

* [Node.js v22+](https://nodejs.org/) installed
* A [Circle Developer Console](https://console.circle.com) account
* An [API key](/build/keys) created in the Console:\
  **Keys → Create a key → API key → Standard Key**
* Your
  [Entity Secret registered](https://developers.circle.com/wallets/dev-controlled/register-entity-secret)

## Install the SDK

Use the following commands to install the SDK. You can
[view the package information on the npm site](https://www.npmjs.com/package/@circle-fin/smart-contract-platform).

<CodeGroup>
  ```shell npm theme={null}
  npm install @circle-fin/smart-contract-platform --save
  ```

  ```shell yarn theme={null}
  yarn add @circle-fin/smart-contract-platform
  ```
</CodeGroup>

## Contracts client

To start using the SDK, you first need to configure a client. Import the
`initiateSmartContractPlatformClient` factory from the SDK, and then initialize
the client using your API key and entity secret.

### Import the client

The following example shows how to import the client and configure it to use
your API key and entity secret:

<CodeGroup>
  ```javascript CommonJS theme={null}
  const {
    initiateSmartContractPlatformClient,
  } = require("@circle-fin/smart-contract-platform");
  const client = initiateSmartContractPlatformClient({
    apiKey: "<your-api-key>",
    entitySecret: "<your-entity-secret>",
  });
  ```

  ```javascript ES Module theme={null}
  import { initiateSmartContractPlatformClient } from "@circle-fin/smart-contract-platform";
  const client = initiateSmartContractPlatformClient({
    apiKey: "<your-api-key>",
    entitySecret: "<your-entity-secret>",
  });
  ```
</CodeGroup>

### Deploy a smart contract

The following example shows how to deploy a smart contract using the client:

```javascript theme={null}
const response = await client.deployContract({
  name: "First Contract",
  description: "My first hello world contract",
  walletId: "004735f6-d9fc-44f8-933c-672cdf3d240d",
  abiJson:
    "[\n\t{\n\t\t'inputs': [],\n\t\t'stateMutability': 'nonpayable',\n\t\t'type': 'constructor'\n\t},\n\t...",
  bytecode: "0x60806040523480156200001157600080fd5b50604051806040...",
  constructorParameters: ["TICK", 10000],
  feeLevel: "MEDIUM",
});
console.log(response.data);
```

## Client configuration options

The client for the Contracts SDK accepts the following configuration parameters:

| **Option** | **Required?** | **Description** |
| - | - | - |
| `apiKey` | Yes | The API key used to authenticate requests to the Circle API. |
| `entitySecret` | Yes | Your configured entity secret. |
| `storage` | No | Optional custom storage solution for persisting data. If not provided, the SDK uses in-memory storage. |