> ## 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. # Get token balances on a remote domain > Returns the expected token balances for a specified remote domain based on the deposit amounts made into xReserve. ## OpenAPI ````yaml openapi/xreserve.yaml get /v1/balances/{remoteDomain} openapi: 3.0.2 info: title: Circle xReserve version: 1.0.0 description: > xReserve enables transfers between USDC and USDC-backed tokens across supported blockchain networks using a secure attestation system. servers: - url: https://xreserve-api-testnet.circle.com description: Testnet - url: https://xreserve-api.circle.com description: Mainnet security: [] tags: - name: xReserve description: xReserve endpoints paths: /v1/balances/{remoteDomain}: get: tags: - xReserve summary: Get token balances on a remote domain description: >- Returns the expected token balances for a specified remote domain based on the deposit amounts made into xReserve. operationId: getBalances parameters: - $ref: '#/components/parameters/RemoteDomain' - $ref: '#/components/parameters/TokenQuery' responses: '200': $ref: '#/components/responses/BalancesResponse' '400': $ref: '#/components/responses/ErrorResponse' '500': $ref: '#/components/responses/ErrorResponse' components: parameters: RemoteDomain: in: path name: remoteDomain required: true schema: type: integer minimum: 0 description: The remote domain ID by which to filter results. example: 1 TokenQuery: in: query name: token required: false schema: type: string description: The token by which to query balances, such as `USDC`. responses: BalancesResponse: description: Successfully retrieved balances. content: application/json: schema: $ref: '#/components/schemas/BalancesResponse' ErrorResponse: description: Standard error response. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' schemas: BalancesResponse: type: object description: Contains token balances for a remote domain. properties: balances: type: array description: List token balance entries. items: type: object properties: token: type: string description: The token symbol. example: USDC balance: type: string description: The token balance amount. example: '1000000' required: - token - balance required: - balances ErrorResponse: type: object description: Standard error response. properties: success: type: boolean example: false message: type: string example: Error message ````