> ## 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.

# AI skills for building with Circle

Use Circle's open source AI skills to accelerate development with AI-assisted
IDEs. Skills provide specialized knowledge for building with Circle's products,
including wallets, crosschain transfers, and smart contracts.

Skills are available in the
[circlefin/skills](https://github.com/circlefin/skills) repository.

## Installation

Use the following commands to install Circle Skills with the command-line.

<CodeGroup>
  ```shell Claude Code icon="https://mintcdn.com/circle-167b8d39/5X_H2DLmIxVDSWCs/images/claude-logo.png?fit=max&auto=format&n=5X_H2DLmIxVDSWCs&q=85&s=2711bd5dc795308c62570a011248ef2d" theme={null}
  /plugin marketplace add circlefin/skills
  /plugin install circle-skills@circle
  ```

  ```shell Vercel Skills CLI icon="https://mintcdn.com/circle-167b8d39/kF52uen9TY9sspam/images/vercel_logo.png?fit=max&auto=format&n=kF52uen9TY9sspam&q=85&s=20d2a3e59acc98f14fe41854458cfcd5" theme={null}
  npx skills add circlefin/skills
  ```
</CodeGroup>

## Available skills

The following skills are available to help you build with Circle's products.

### `accept-agent-payments`

Monetize an API by charging AI agents per request in USDC over
[x402](/x402-facilitators/x402). Scaffolds both payment rails (Gateway
nanopayments and vanilla x402) and prepares your service for the
[Agent Marketplace](/agent-stack/agent-marketplace).

### `bridge-stablecoin`

Build apps that bridge USDC between chains using Circle's
[Cross-Chain Transfer Protocol (CCTP)](/cctp). Includes UX patterns, progress
tracking, destination chain linking, and
[Bridge Kit](https://docs.arc.io/app-kit/bridge) SDK implementation patterns for
EVM and Solana chains.

### `use-arc`

Build on Arc, Circle's blockchain where USDC is the native gas token. Covers
chain configuration, [smart contract](/contracts) deployment with Foundry or
Hardhat, frontend integration with viem/wagmi, and bridging USDC to Arc via
[CCTP](/cctp).

### `use-circle-wallets`

Choose the right [Circle wallet](/wallets) type for your application. Compares
[developer-controlled](/wallets/dev-controlled),
[user-controlled](/wallets/user-controlled), and [modular](/wallets/modular)
(passkey) wallets across custody model, key management, account types, and
blockchain support.

### `use-developer-controlled-wallets`

[Developer-controlled wallets](/wallets/dev-controlled) where developers manage
wallet creation, storage, and key management. Use for custodial or operational
flows like payouts, treasury movements, subscriptions, and automation.

### `use-gateway`

Implement [Circle Gateway](/gateway) unified balance for crosschain USDC
transfers. Supports instant transfers (under 500ms) across EVM and Solana chains
with deposit, balance query, and transfer workflows.

### `use-modular-wallets`

Build [modular wallets](/wallets/modular) with passkey authentication, gasless
transactions, and modular architecture. Supports ERC-4337 account abstraction
and ERC-6900 modular framework.

### `use-smart-contract-platform`

Deploy, import, interact with, and monitor smart contracts using
[Circle's Smart Contract Platform](/contracts). Supports bytecode deployment,
template contracts (ERC-20/721/1155), ABI-based read/write calls, and event
monitoring.

### `use-user-controlled-wallets`

Build embedded [user-controlled wallets](/wallets/user-controlled) where users
control their own assets. Supports Web2-like login experiences (Google,
Facebook, Apple, email OTP, PIN) without seed phrases.