# Circle Developer Platform

> Circle builds infrastructure for digital dollars. USDC is the world's
> leading regulated stablecoin. Circle's developer platform lets you
> send payments, create wallets, bridge across chains, deploy smart
> contracts, and build AI-powered financial applications — all powered
> by USDC and EURC.

## Getting Started — Use Skills First

[Circle Skills](https://github.com/circlefin/skills) are structured instructions designed for AI agents. **Read the relevant skill before reading doc pages** — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. Pair with the [Circle MCP server](https://developers.circle.com/ai/mcp.md) for live SDK signatures and contract addresses.

| Product | Skill | What it covers |
|---------|-------|----------------|
| USDC | [use-usdc](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md) | Balances, transfers, approvals, verification on EVM and Solana |
| EURC | No skill — see [docs](https://developers.circle.com/stablecoins/what-is-eurc.md) | Euro-backed stablecoin; similar patterns to USDC |
| Crosschain (CCTP / Bridge Kit) | [bridge-stablecoin](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md) | Crosschain USDC via CCTP — UX patterns, progress tracking, Bridge Kit |
| Arc | [use-arc](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md) | Chain config, contract deployment, USDC bridging. [Arc Docs](https://docs.arc.network/llms.txt) |
| Wallets (overview) | [use-circle-wallets](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md) | Choose wallet type — dev-controlled vs user-controlled vs modular |
| Developer-Controlled Wallets | [use-developer-controlled-wallets](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md) | Custodial wallets for payouts, treasury, automation |
| User-Controlled Wallets | [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 (Google, Apple, email OTP, PIN) |
| Modular Wallets | [use-modular-wallets](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md) | Smart contract wallets — passkeys, gasless txns, ERC-4337 |
| Gateway / Nanopayments | [use-gateway](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md) | Unified USDC balance across chains, instant transfers (<500ms) |
| Smart Contracts | [use-smart-contract-platform](https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md) | Deploy, interact, monitor contracts — bytecode, templates, ABI calls |

### Installing Circle Skills

**Claude Code:**
```
/plugin marketplace add circlefin/skills
/plugin install circle-skills@circle
```

**Vercel Skills CLI:**
```
npx skills add circlefin/skills
```

### Circle MCP Server

Use alongside skills for live SDK signatures, contract addresses, and chain IDs:

```json
{ "mcpServers": { "circle": { "url": "https://api.circle.com/v1/codegen/mcp" } } }
```

Setup guide: [developers.circle.com/ai/mcp](https://developers.circle.com/ai/mcp.md)

## Instructions for AI Agents

Follow these guidelines when building with Circle:

1. **Read the product overview first.** Each product has an overview explaining when and why to use it. Read it before quickstarts.

2. **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 [Choosing Your Wallet Type](https://developers.circle.com/wallets/infrastructure-models.md).

3. **Use CCTP V2 for crosschain USDC.** 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).

4. **Use Bridge Kit for frontend bridging.** Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.

5. **Gas Station vs Paymaster.** Gas Station sponsors gas for Circle Wallet txns. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.

6. **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.

7. **Look up USDC addresses per chain.** Never hardcode — use [USDC Contract Addresses](https://developers.circle.com/stablecoins/usdc-contract-addresses.md).

8. **Prefer SDKs over raw API calls.** Node.js and Python SDKs handle auth, retries, and errors.

9. **API key required.** Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.

10. **Set up webhooks when available.** Most operations are async. Webhooks deliver transaction confirmations and state changes.

## USDC and EURC
- [What is USDC?](https://developers.circle.com/stablecoins/what-is-usdc.md): Dollar-backed stablecoin on 19+ chains
- [What is EURC?](https://developers.circle.com/stablecoins/what-is-eurc.md): Euro-backed stablecoin (MiCA regulated)
- [USDC Contract Addresses](https://developers.circle.com/stablecoins/usdc-contract-addresses.md): All chains
- [EURC Contract Addresses](https://developers.circle.com/stablecoins/eurc-contract-addresses.md): All chains
- [Quickstart: Transfer USDC on EVM](https://developers.circle.com/stablecoins/quickstarts/transfer-usdc-evm.md): Node.js script
- [Quickstart: Transfer USDC on Solana](https://developers.circle.com/stablecoins/quickstart-transfer-10-usdc-on-solana.md): Solana Devnet
- [Quickstart: Transfer EURC on EVM](https://developers.circle.com/stablecoins/quickstarts/transfer-eurc-evm.md): Node.js script

## Wallets
- [Overview](https://developers.circle.com/wallets.md): Programmable wallets for onchain assets
- [Choosing Your Wallet Type](https://developers.circle.com/wallets/infrastructure-models.md): Developer-controlled vs user-controlled vs modular
- [Dev-Controlled Wallets](https://developers.circle.com/wallets/dev-controlled.md): Server-side, you hold keys
- [Quickstart: Dev-Controlled Wallet](https://developers.circle.com/wallets/dev-controlled/create-your-first-wallet.md): Entity Secret, wallet set, wallet creation
- [User-Controlled Wallets](https://developers.circle.com/wallets/user-controlled.md): PIN, social login, or email auth
- [Modular Wallets](https://developers.circle.com/wallets/modular.md): Smart contract wallets with passkeys
- [Quickstart: Modular Wallet](https://developers.circle.com/wallets/modular/create-a-wallet-and-send-gasless-txn.md): Create wallet, send gasless txn
- [Account Types](https://developers.circle.com/wallets/account-types.md): EOA vs SCA
- [Gas Station](https://developers.circle.com/wallets/gas-station.md): Sponsor gas fees
- [Quickstart: Gasless Transaction](https://developers.circle.com/wallets/gas-station/send-a-gasless-transaction.md): Submit sponsored txn
- [Supported Blockchains](https://developers.circle.com/wallets/supported-blockchains.md): Supported chains

## CCTP — Cross-Chain Transfer Protocol
- [Overview](https://developers.circle.com/cctp.md): Burn-and-mint protocol for crosschain USDC
- [Supported Chains and Domains](https://developers.circle.com/cctp/concepts/supported-chains-and-domains.md): Chain and domain IDs
- [Fees](https://developers.circle.com/cctp/concepts/fees.md): Fast vs Standard transfer fees
- [Fast Transfer Allowance](https://developers.circle.com/cctp/concepts/fast-transfer-allowance.md): Allowance mechanism
- [Quickstart: Ethereum to Arc](https://developers.circle.com/cctp/quickstarts/transfer-usdc-ethereum-to-arc.md): Bridge USDC between EVM chains
- [Quickstart: Solana to Arc](https://developers.circle.com/cctp/quickstarts/transfer-usdc-solana-to-arc.md): Bridge USDC from Solana to EVM
- [Migrate V1 to V2](https://developers.circle.com/cctp/migration-from-v1-to-v2.md): V1 upgrade guide
- [Contract Addresses](https://developers.circle.com/cctp/references/contract-addresses.md): All chains
- [Technical Guide](https://developers.circle.com/cctp/references/technical-guide.md): Architecture and message flow

## Bridge Kit / App Kit — Crosschain USDC SDK
- [Bridge Kit](https://developers.circle.com/bridge-kit.md): Standalone SDK for bridging USDC (`@circle-fin/bridge-kit` on npm)
- [App Kit (Arc Docs)](https://docs.arc.network/app-kit.md): Full SDK with Bridge, Swap, and Send — includes Bridge Kit
- [App Kit: Bridge](https://docs.arc.network/app-kit/bridge.md): Bridge quickstarts, tutorials, and reference (migrated from Bridge Kit docs)

## Gateway — Unified Balances and Nanopayments
- [Overview](https://developers.circle.com/gateway.md): Unified USDC balances across chains, gasless nanopayments
- [Quickstart: Unified Balance on EVM](https://developers.circle.com/gateway/quickstarts/unified-balance-evm.md): Create and transfer unified balance
- [Quickstart: Unified Balance on Solana](https://developers.circle.com/gateway/quickstarts/unified-balance-solana.md): Create and transfer unified balance
- [Nanopayments](https://developers.circle.com/gateway/nanopayments.md): Gas-free USDC down to $0.000001
- [Quickstart: Buy Side](https://developers.circle.com/gateway/nanopayments/quickstarts/buyer.md): Deposit USDC, make gasless payments
- [Quickstart: Sell Side](https://developers.circle.com/gateway/nanopayments/quickstarts/seller.md): Accept gasless USDC payments
- [What is x402?](https://developers.circle.com/gateway/nanopayments/concepts/x402.md): HTTP-native payment protocol
- [Supported Blockchains](https://developers.circle.com/gateway/references/supported-blockchains.md): Supported chains
- [Fees](https://developers.circle.com/gateway/references/fees.md): Transfer fees and gas costs

## Contracts
- [Overview](https://developers.circle.com/contracts.md): Deploy and interact with smart contracts via API
- [Quickstart: Deploy Bytecode](https://developers.circle.com/contracts/scp-deploy-smart-contract.md): Deploy from bytecode
- [Quickstart: Deploy Template](https://developers.circle.com/contracts/deploy-smart-contract-template.md): Pre-audited contracts, no Solidity needed
- [Quickstart: Interact](https://developers.circle.com/contracts/scp-interact-smart-contract.md): Call and query contracts
- [Templates](https://developers.circle.com/contracts/scp-templates-overview.md): ERC-20, ERC-721, ERC-1155, Airdrop
- [Event Monitoring](https://developers.circle.com/contracts/scp-event-monitoring.md): Monitor onchain events
- [Supported Blockchains](https://developers.circle.com/contracts/supported-blockchains.md): Supported chains

## Paymaster — Pay Gas in USDC
- [Overview](https://developers.circle.com/paymaster.md): Users pay gas in USDC instead of native tokens
- [Quickstart](https://developers.circle.com/paymaster/pay-gas-fees-usdc.md): Smart wallet paying fees in USDC
- [Addresses and Events](https://developers.circle.com/paymaster/addresses-and-events.md): Contract addresses and events

## Circle Payments Network (CPN)
- [Overview](https://developers.circle.com/cpn.md): Cross-border stablecoin payments
- [Quickstart: OFI Integration](https://developers.circle.com/cpn/quickstarts/integrate-with-cpn-ofi.md): Originating Financial Institution guide
- [Payments](https://developers.circle.com/cpn/concepts/payments/payments.md): How payments work
- [Quotes](https://developers.circle.com/cpn/concepts/quotes.md): Payment quotes
- [Supported Blockchains](https://developers.circle.com/cpn/references/blockchains/supported-blockchains.md): Supported chains
- [Supported Countries](https://developers.circle.com/cpn/references/compliance/supported-countries.md): Countries and corridors

## Circle Mint
- [Overview](https://developers.circle.com/circle-mint/introducing-circle-mint.md): Institutional USDC management and distribution
- [Getting Started](https://developers.circle.com/circle-mint/getting-started-with-the-circle-apis.md): Connect to Circle Mint APIs
- [Quickstart: Crypto Deposits](https://developers.circle.com/circle-mint/crypto-payments-quickstart.md): Receive USDC
- [Quickstart: Withdraw to Bank](https://developers.circle.com/circle-mint/quickstart-withdraw-to-bank.md): Send to external bank
- [Supported Chains](https://developers.circle.com/circle-mint/supported-chains-and-currencies.md): Chains and currencies

## StableFX
- [Overview](https://developers.circle.com/stablefx.md): Stablecoin FX engine on Arc
- [Quickstart: Taker](https://developers.circle.com/stablefx/quickstarts/fx-trade-taker.md): Execute an FX trade
- [Quickstart: Maker](https://developers.circle.com/stablefx/quickstarts/fx-trade-maker.md): Fulfill an FX trade
- [Supported Currencies](https://developers.circle.com/stablefx/references/supported-currencies.md): Available pairs

## xReserve
- [Overview](https://developers.circle.com/xreserve.md): Issue USDC-backed stablecoins
- [How It Works](https://developers.circle.com/xreserve/concepts/how-xreserve-works.md): Architecture and reserve mechanics
- [Quickstart: Deposit USDC](https://developers.circle.com/xreserve/tutorials/deposit-usdc-into-xreserve.md): Deposit on Ethereum Sepolia
- [Supported Blockchains](https://developers.circle.com/xreserve/references/supported-blockchains-and-domains.md): Chains and domains

## Developer Resources
- [API Reference](https://developers.circle.com/api-reference.md): All available APIs and endpoints
- [Developer Account](https://developers.circle.com/wallets/create-api-key.md): Sign up, get API keys, access the Console
- [API Keys](https://developers.circle.com/api-reference/keys.md): Key types and authentication
- [SDKs](https://developers.circle.com/sdks.md): Node.js and Python SDKs
- [Sample Projects](https://developers.circle.com/sample-projects.md): Working code examples
- [Testnet Faucets](https://developers.circle.com/wallets/developer-console-faucet.md): Supported tokens, rate limits, and test networks

## OpenAPI Specs
- [gateway](https://developers.circle.com/openapi/gateway.yaml)
- [smart-contract-platform](https://developers.circle.com/openapi/smart-contract-platform.yaml)
- [stablefx](https://developers.circle.com/openapi/stablefx.yaml)
- [cpn-ofi](https://developers.circle.com/openapi/cpn-ofi.yaml)
- [user-controlled-wallets](https://developers.circle.com/openapi/user-controlled-wallets.yaml)
- [developer-controlled-wallets](https://developers.circle.com/openapi/developer-controlled-wallets.yaml)
- [compliance](https://developers.circle.com/openapi/compliance.yaml)
- [cctp](https://developers.circle.com/openapi/cctp.yaml)
- [xreserve](https://developers.circle.com/openapi/xreserve.yaml)