> ## 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. # Estimate fee for a transfer transaction > Estimates gas fees that will be incurred for a transfer transaction; given its amount, blockchain, and token. ## OpenAPI ````yaml openapi/developer-controlled-wallets.yaml post /v1/w3s/transactions/transfer/estimateFee openapi: 3.0.3 info: version: '1.0' title: Developer-Controlled Wallets description: Developer-Controlled Wallets API documentation. servers: - url: https://api.circle.com security: - BearerAuth: [] tags: - name: Wallet Sets - name: Wallets - name: Signing - name: Transactions - name: Token Lookup paths: /v1/w3s/transactions/transfer/estimateFee: post: tags: - Transactions summary: Estimate fee for a transfer transaction description: >- Estimates gas fees that will be incurred for a transfer transaction; given its amount, blockchain, and token. operationId: createTransferEstimateFee parameters: - $ref: '#/components/parameters/XRequestId' requestBody: $ref: '#/components/requestBodies/EstimateTransferTransactionFee' responses: '200': content: application/json: schema: $ref: '#/components/schemas/EstimateTransactionFee' description: Transaction fee estimated headers: X-Request-Id: $ref: '#/components/headers/XRequestId' '400': $ref: '#/components/responses/DefaultError' '404': $ref: '#/components/responses/NotFound' security: - BearerAuth: [] components: parameters: 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' requestBodies: EstimateTransferTransactionFee: content: application/json: schema: title: EstimateTransferTransactionFeeRequest type: object required: - amounts - destinationAddress properties: amounts: $ref: '#/components/schemas/TransferAmounts-2' destinationAddress: $ref: '#/components/schemas/Address' nftTokenIds: $ref: '#/components/schemas/NftTokenIds' sourceAddress: $ref: '#/components/schemas/SourceAddress' tokenId: $ref: '#/components/schemas/TokenId' tokenAddress: $ref: '#/components/schemas/TokenAddress' blockchain: $ref: '#/components/schemas/TokenBlockchain' walletId: $ref: '#/components/schemas/WalletId' description: Estimate transaction fee request required: true schemas: EstimateTransactionFee: title: EstimateTransactionFeeResponse type: object required: - data properties: data: type: object properties: high: $ref: '#/components/schemas/TransactionFee' low: $ref: '#/components/schemas/TransactionFee' medium: $ref: '#/components/schemas/TransactionFee' callGasLimit: $ref: '#/components/schemas/CallGasLimit' verificationGasLimit: $ref: '#/components/schemas/VerificationGasLimit' preVerificationGas: $ref: '#/components/schemas/PreVerificationGas' 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 TransferAmounts-2: title: TransferAmounts type: array items: type: string description: >- Transfer amounts in decimal number format, at least one element is required for transfer. For ERC721 token transfer, the amounts field is required to be ["1"] (array with "1" as the only element). example: - '6.62607015' minItems: 1 Address: title: Address description: > Blockchain generated unique identifier, associated with wallet (account), smart contract or other blockchain objects. type: string example: '0xca9142d0b9804ef5e239d3bc1c7aa0d1c74e7350' NftTokenIds: title: NftTokenIds type: array description: >- List of NFT token IDs corresponding with the NFTs to transfer. Batch transfers are supported only for ERC-1155 tokens. The length of NFT token IDs must match the length of amounts. items: $ref: '#/components/schemas/NftTokenId' SourceAddress: type: string description: > Source address of the transaction. Required along with `blockchain` if `walletId` is not provided. The `sourceAddress` and `walletId` fields are mutually exclusive. example: '0x1bf9ad0cc2ad298c69a2995aa806ee832788218c' TokenId: title: TokenId type: string format: uuid description: >- System generated identifier of the token. Excluded with `tokenAddress` and `tokenBlockchain`. TokenAddress: title: TokenAddress type: string description: >- Blockchain address of the transferred token. Empty for native tokens. Excluded with `tokenId`. TokenBlockchain: title: TokenBlockchain type: string description: > Blockchain of the transferred token. Required if `tokenId` is not provided. The `blockchain` and `tokenId` fields are mutually exclusive. enum: - ETH - ETH-SEPOLIA - AVAX - AVAX-FUJI - MATIC - MATIC-AMOY - SOL - SOL-DEVNET - ARB - ARB-SEPOLIA - UNI - UNI-SEPOLIA - BASE - BASE-SEPOLIA - OP - OP-SEPOLIA - APTOS - APTOS-TESTNET - ARC - ARC-TESTNET - MONAD - MONAD-TESTNET example: MATIC-AMOY WalletId: title: WalletId type: string format: uuid description: | Unique system generated identifier of the wallet. For contract deploys this wallet ID will be used as the source. example: a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11 TransactionFee: type: object properties: gasLimit: $ref: '#/components/schemas/GasLimit' gasPrice: $ref: '#/components/schemas/GasPrice' maxFee: $ref: '#/components/schemas/MaxFee' priorityFee: $ref: '#/components/schemas/PriorityFee' baseFee: $ref: '#/components/schemas/BaseFee' networkFee: $ref: '#/components/schemas/NetworkFee' networkFeeRaw: $ref: '#/components/schemas/NetworkFeeRaw' l1Fee: $ref: '#/components/schemas/L1Fee' CallGasLimit: title: CallGasLimit type: string description: >- One of ERC-4337 gas fields. The amount of gas to allocate for the main execution call. Only in smart contract account estimation response. example: '69222' VerificationGasLimit: title: VerificationGasLimit type: string description: >- One of ERC-4337 gas fields. The amount of gas to allocate for the verification step. Only in smart contract account estimation response. example: '56863' PreVerificationGas: title: PreVerificationGas type: string description: >- One of ERC-4337 gas fields. The amount of gas to pay to compensate the bundler for pre-verification execution and call data. Only in smart contract account estimation response. example: '44112' 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. NftTokenId: title: NftTokenId type: string description: The NFT token ID. example: '2' GasLimit: type: string description: > The maximum units of gas to use for the transaction. Required if `feeLevel` is not provided. Estimates for this limit can be obtained through the [`POST /transactions/transfer/estimateFee`](/api-reference/w3s/developer-controlled-wallets/create-transfer-estimate-fee) API. An insufficient gas limit may cause the transaction to fail on-chain. Use this field with care when manually providing values. GasLimit override (only supported for EOA wallets): Using `gasLimit` together with `feeLevel`, the provided `gasLimit` will override the estimation's gasLimit. example: '21000' GasPrice: type: string description: > For blockchains without EIP-1559 support, the maximum price of gas, in gwei, to use per each unit of gas (see `gasLimit`). Requires `gasLimit`. Cannot be used with `feeLevel`, `priorityFee`, or `maxFee`. Estimates for this fee can be obtained through the [`POST /transactions/transfer/estimateFee`](/api-reference/w3s/developer-controlled-wallets/create-transfer-estimate-fee) API. The wallet service enforces a dynamic minimum `gasPrice` based on current network conditions. Requests specifying a `gasPrice` below this minimum will be rejected MaxFee: type: string example: '5.935224468' description: > For blockchains with EIP-1559 support, the maximum price per unit of gas (see `gasLimit`), in gwei. Requires `priorityFee`, and `gasLimit` to be present. Cannot be used with `feeLevel` or `gasPrice`. Estimates for this fee can be obtained through the [`POST /transactions/transfer/estimateFee`](/api-reference/w3s/developer-controlled-wallets/create-transfer-estimate-fee) API. PriorityFee: type: string example: '1.022783914' description: > For blockchains with EIP-1559 support, the “tip”, in gwei, to add to the base fee as an incentive for validators. Please note that the `maxFee` and `gasLimit` parameters are required alongside the `priorityFee`. The `feeLevel` and `gasPrice` parameters cannot be used with the `priorityFee`. Estimations for this fee can be obtained through the [`POST /transactions/transfer/estimateFee`](/api-reference/w3s/developer-controlled-wallets/create-transfer-estimate-fee) API. The wallet service enforces a dynamic minimum `priorityFee` based on current network conditions. Requests specifying a `priorityFee` below this minimum will be rejected BaseFee: type: string example: '1.022783914' description: > For blockchains with EIP-1559 support, the estimated base fee represents the minimum fee required for a transaction to be included in a block on the blockchain. It is measured in gwei and compensates for the computational resources validators consume to process the transaction. The base fee is supplemented by a separate "tip" called the priority fee, which acts as an extra incentive for validators to prioritize the transaction. The priority fee is added to the base fee to calculate the final transaction fee. NetworkFee: type: string example: '0.0001246397138' description: > The estimated network fee is the maximum amount of cryptocurrency (such as ETH, ARB, or SOL) that you will pay for your transaction. This fee depends on the parameters you set, including Gas Limit, Priority Fee, and Max Fee. It compensates for the computational resources that validators consume to process the transaction. It is measured in native token such as ETH, SOL. For blockchains with L1 data fees such as OP/BASE, the network fee is a combination of the Execution Gas Fee and the L1 Data Fee. Each blockchain might use different formula for network fee. Refer to each specific blockchain's documentation to understand how `networkFee` is calculated. NetworkFeeRaw: type: string example: '0.0001246397138' description: > Similar to `networkFee`, `networkFeeRaw` is an estimation with lower buffer and thus should be closer to the actual on-chain expense. This field will only be returned in the estimation response. L1Fee: type: string example: '0.000000000000140021' description: > This fee represents the Layer 1 (L1) rollup charge associated with transactions on Layer 2 blockchains. The amount is expressed in the native currency, such as ETH. This field is relevant for Layer 2 blockchains utilizing a rollup mechanism and for specific account types, such as externally owned accounts (EOAs) on the Optimism (OP) blockchain. 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' responses: DefaultError: content: application/json: schema: $ref: '#/components/schemas/Error' description: Error response 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. ````