> ## 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 balance for a wallet > Fetches the digital asset balance for a single user-controlled wallet using its unique identifier. **Note**: On Aptos, this endpoint only returns balances for tokens stored in primary storage. Tokens held in [AIP-21](https://github.com/aptos-labs/aptos-core/releases/tag/aptos-node-v1.5.0) secondary storage are excluded from balance queries and deposit notifications to prevent incorrect or misleading results from secondary storage-based state changes. ## OpenAPI ````yaml openapi/user-controlled-wallets.yaml get /v1/w3s/wallets/{id}/balances openapi: 3.0.3 info: version: '1.0' title: User-Controlled Wallets description: User-Controlled Wallets API documentation. servers: - url: https://api.circle.com security: - BearerAuth: [] tags: - name: Social/ Email Authentication - name: PIN Authentication - name: Users - name: Wallets - name: Transactions - name: Token Lookup - name: Signing paths: /v1/w3s/wallets/{id}/balances: get: tags: - Wallets summary: Get token balance for a wallet description: >- Fetches the digital asset balance for a single user-controlled wallet using its unique identifier. **Note**: On Aptos, this endpoint only returns balances for tokens stored in primary storage. Tokens held in [AIP-21](https://github.com/aptos-labs/aptos-core/releases/tag/aptos-node-v1.5.0) secondary storage are excluded from balance queries and deposit notifications to prevent incorrect or misleading results from secondary storage-based state changes. operationId: listWalletBalance parameters: - $ref: '#/components/parameters/XUserToken' - description: Wallet ID in: path name: id required: true schema: type: string - $ref: '#/components/parameters/IncludeAll' - $ref: '#/components/parameters/TokenName' - $ref: '#/components/parameters/TokenAddress' - $ref: '#/components/parameters/TokenStandard' - $ref: '#/components/parameters/PageBefore' - $ref: '#/components/parameters/PageAfter' - $ref: '#/components/parameters/PageSize' - $ref: '#/components/parameters/XRequestId' responses: '200': content: application/json: schema: $ref: '#/components/schemas/Balances' description: Success headers: X-Request-Id: $ref: '#/components/headers/XRequestId' Link: $ref: '#/components/headers/PaginationLink' '400': $ref: '#/components/responses/DefaultError' '401': $ref: '#/components/responses/NotAuthorized' '404': $ref: '#/components/responses/NotFound' security: - BearerAuth: [] components: parameters: XUserToken: name: X-User-Token description: Unique system generated JWT session token for specific user. required: true in: header schema: type: string IncludeAll: name: includeAll description: Return all recourses with monitored and non-monitored tokens. in: query required: false schema: type: boolean example: true TokenName: name: name description: Filter by token name. in: query schema: type: string TokenAddress: name: tokenAddress description: Filter by token address. in: query schema: $ref: '#/components/schemas/Address' TokenStandard: name: standard description: >- Filter by the token standard. ERC20/ERC721/ERC1155 are the standards for EVM chains, Fungible/FungibleAsset/NonFungible/NonFungibleEdition/ProgrammableNonFungible/ProgrammableNonFungibleEdition are the standards for the Solana chain, FungibleAsset is the standard for the Aptos chain. in: query schema: $ref: '#/components/schemas/TokenStandard' PageBefore: name: pageBefore description: > A collection ID value used for pagination. It marks the exclusive end of a page. When provided, the collection resource will return the next n items before the id, with n being specified by pageSize. The items will be returned in the natural order of the collection. The resource will return the first page if neither pageAfter nor pageBefore are specified. SHOULD NOT be used in conjunction with pageAfter. in: query schema: type: string format: uuid PageAfter: name: pageAfter description: > A collection ID value used for pagination. It marks the exclusive begin of a page. When provided, the collection resource will return the next n items after the id, with n being specified by pageSize. The items will be returned in the natural order of the collection. The resource will return the first page if neither pageAfter nor pageBefore are specified. SHOULD NOT be used in conjunction with pageBefore. in: query schema: type: string format: uuid PageSize: name: pageSize description: > Limits the number of items to be returned. Some collections have a strict upper bound that will disregard this value. In case the specified value is higher than the allowed limit, the collection limit will be used. If avoided, the collection will determine the page size itself. in: query schema: type: integer default: 10 maximum: 50 minimum: 1 XRequestId: name: X-Request-Id in: header description: > Developer-provided identifier for this request, used for tracing requests in Wallets API logs and the Developer Console, and when communicating with Circle Support. **Must be a UUID to appear in logs.** Non-UUID values are accepted by the API but are ignored by logging and tracing systems. schema: $ref: '#/components/schemas/XRequestId' schemas: Balances: title: BalancesResponse type: object required: - data properties: data: type: object properties: tokenBalances: description: List of token balances for each token on the wallet(s). type: array items: $ref: '#/components/schemas/Balance' Address: title: Address description: > Blockchain generated unique identifier, associated with wallet (account), smart contract or other blockchain objects. type: string example: '0xca9142d0b9804ef5e239d3bc1c7aa0d1c74e7350' TokenStandard: title: TokenStandard type: string enum: - ERC20 - ERC721 - ERC1155 - Fungible - FungibleAsset - NonFungible - NonFungibleEdition - ProgrammableNonFungible - ProgrammableNonFungibleEdition XRequestId: type: string format: uuid description: >- A unique identifier, which can be helpful for identifying a request when communicating with Circle support. example: 2adba88e-9d63-44bc-b975-9b6ae3440dde Balance: title: Balance type: object required: - token - updateDate - amount properties: amount: type: string description: Token balance for each token in the wallet. example: '6.62607015' token: $ref: '#/components/schemas/Token' updateDate: $ref: '#/components/schemas/UpdateDate' Error: title: Error type: object required: - code - message properties: code: type: integer description: Code that corresponds to the error. message: type: string description: Message that describes the error. Token: title: Token type: object required: - id - blockchain - isNative - createDate - updateDate properties: id: $ref: '#/components/schemas/Id' name: type: string description: Blockchain name of the specified token. standard: $ref: '#/components/schemas/TokenStandard' blockchain: $ref: '#/components/schemas/Blockchain' decimals: type: integer description: Number of decimal places shown in the token amount. isNative: type: boolean description: >- Defines if the token is a native token of the specified blockchain. If TRUE, the token is a native token. symbol: type: string description: Blockchain symbol of the specified token. tokenAddress: $ref: '#/components/schemas/Address' updateDate: $ref: '#/components/schemas/UpdateDate' createDate: $ref: '#/components/schemas/CreateDate' UpdateDate: type: string format: date-time description: Date and time the resource was last updated, in ISO-8601 UTC format. example: '2023-01-01T12:04:05Z' Id: type: string format: uuid description: System-generated unique identifier of the resource. example: c4d1da72-111e-4d52-bdbf-2e74a2d803d5 Blockchain: type: string description: >- The blockchain network that the resource is to be created on or is currently on. enum: - ETH - ETH-SEPOLIA - AVAX - AVAX-FUJI - MATIC - MATIC-AMOY - SOL - SOL-DEVNET - ARB - ARB-SEPOLIA - NEAR - NEAR-TESTNET - EVM - EVM-TESTNET - UNI - UNI-SEPOLIA - BASE - BASE-SEPOLIA - OP - OP-SEPOLIA - APTOS - APTOS-TESTNET - ARC - ARC-TESTNET - MONAD - MONAD-TESTNET example: MATIC-AMOY CreateDate: type: string format: date-time description: Date and time the resource was created, in ISO-8601 UTC format. example: '2023-01-01T12:04:05Z' headers: XRequestId: description: > Developer-provided header parameter or Circle-generated universally unique identifier (UUID v4). Useful for identifying a specific request when communicating with Circle Support. schema: $ref: '#/components/schemas/XRequestId' PaginationLink: description: > Pagination cursor information. Format includes the following link relations: - self: URL pointing to the current page. - first: URL pointing to the first page. - next: URL pointing to the next page (omitted on the last page). - prev: URL pointing to the previous page (omitted on the first page). It's important to form calls with Link header values instead of constructing your own URLs. schema: type: string example: >- ; rel="next" responses: DefaultError: content: application/json: schema: $ref: '#/components/schemas/Error' description: Error response headers: X-Request-Id: $ref: '#/components/headers/XRequestId' NotAuthorized: content: application/json: schema: type: object title: NotAuthorizedResponse required: - code - message properties: code: type: integer description: Code that corresponds to the error. message: type: string description: Message that describes the error. example: code: 401 message: Malformed authorization. description: >- Request has not been applied because it lacks valid authentication credentials. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' NotFound: content: application/json: schema: type: object title: NotFoundResponse required: - code - message properties: code: type: integer description: Code that corresponds to the error. message: type: string description: Message that describes the error. example: code: 404 message: Not found. description: Specified resource was not found. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' securitySchemes: BearerAuth: type: http scheme: bearer bearerFormat: PREFIX:ID:SECRET description: >- Circle's API Keys are formatted in the following structure "PREFIX:ID:SECRET". All three parts are required to make a successful request. ````