> ## 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.

# How-to: Create an API key

> Create an API key in the Circle Console to authenticate Smart Contract Platform API requests.

## Overview

Create an API key so your server-side applications can authenticate requests to
Circle's APIs. You can create and manage API keys in the
[Circle Console](https://console.circle.com/).

## Prerequisites

Before you begin, ensure you have:

* Signed up for a Circle Developer account at
  [console.circle.com/signup](https://console.circle.com/signup)
* Reviewed the [Keys](/api-reference/keys) page for background on key types and
  authentication

## Steps

### Step 1. Open the API & Client Keys page

Sign in to the [Circle Console](https://console.circle.com/) and select **API &
Client Keys** from the left sidebar.

### Step 2. Create a key

Select **Create a key**, then choose **API Key**.

Enter a name for your API key and select the access level:

* **Standard**: grants read/write access to all APIs, including newly introduced
  endpoints.
* **Restricted Access**: limits the key to specific products and permission
  levels.

When you choose restricted access, configure the following options.

Select the products the key can access:

* **Webhooks**: endpoints for
  [webhook subscriptions](/api-reference/wallets/common/create-subscription).
* **Wallets**: all endpoints for
  [user-controlled](/api-reference/wallets/user-controlled-wallets/create-user)
  and developer-controlled wallets.
* **Contracts**: endpoints for
  [smart contracts](/api-reference/contracts/smart-contract-platform/import-contract).
* **Swap Kit**: endpoints for [Swap](https://docs.arc.io/app-kit/swap) in Arc
  App Kits.

Set the permission level for each product:

* **No permission**: the key cannot call any endpoints for that product.
* **Read**: the key can call read-only GET endpoints.
* **Read/Write**: the key can call all endpoints.

<Note>
  You can also add IP addresses or ranges to the IP allowlist for additional
  security.
</Note>

### Step 3. Copy your API key

After the Console confirms that your key was generated, select **Show** to
reveal the key value. Copy it and store it securely. You need it to authenticate
API requests.