> ## 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: Rotate an mTLS API key > Rotate your API key for an mTLS-enabled Circle Mint entity before the mandatory 180-day expiration. API keys on mTLS-enabled entities carry a maximum lifetime of 180 days, whether you enabled mTLS optionally or under MiCA. API keys that exceed this limit are automatically invalidated. This guide walks you through generating a replacement key and rotating your integration with zero downtime. ## Prerequisites Before you begin, ensure that you've: * [Configured mTLS on your entity](/circle-mint/set-up-mtls-authentication) and have a working integration. * Configured access to the [Mint Console](https://app.circle.com) as an Administrator with multi-factor authentication (MFA). ## Steps 1. Sign in to the [Mint Console](https://app.circle.com). 2. Complete the MFA challenge. MFA is required for all API key operations on mTLS-enabled entities. 3. Generate a new API key and store it securely. Generate the new key well in advance of the 180-day expiration. After 180 days, the old key is automatically invalidated and can no longer authenticate requests. Replace the `Authorization: Bearer` header value in your integration with the new API key. For example, update the environment variable or secrets manager entry that stores your key: ```text theme={null} YOUR_API_KEY=your-new-api-key ``` Send a test request using the new API key and your existing client certificate to confirm the new key works. The example below uses `api-eu.circle.com` (the MiCA-regulated hostname). If you enabled mTLS optionally, substitute `api.circle.com`: ```bash theme={null} curl -v --cert /path/to/client-fullchain.pem \ --key /path/to/client-key.pem \ --request GET \ --url https://api-eu.circle.com/v1/businessAccount/balances \ --header "Authorization: Bearer ${YOUR_API_KEY}" ``` Look for `SSL connection using TLSv1.3` in the verbose output and confirm you receive a successful response. If you receive a `401` error, verify that you copied the new key correctly. After you confirm the new key is working in your integration: 1. Sign in to the [Mint Console](https://app.circle.com). 2. Complete the MFA challenge. 3. Revoke the old API key. Do not revoke the old key until you have verified that the new key works. Revoking the old key is irreversible.