> ## 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. # Create an external entity > Creates an external entity for the institutional account. To access the Core API for Institutions, contact your Circle account representative. ## OpenAPI ````yaml openapi/institutional.yaml post /v1/externalEntities openapi: 3.0.2 info: version: ${version} title: Core API for Institutions description: >- The Circle Institutional API provides endpoints for the distribution of USDC to end institutions. servers: - url: https://api-sandbox.circle.com - url: https://api.circle.com security: [] tags: - name: External Entities description: Manage your external entities. paths: /v1/externalEntities: post: tags: - External Entities summary: Create an external entity description: > Creates an external entity for the institutional account. To access the Core API for Institutions, contact your Circle account representative. operationId: createExternalEntity requestBody: content: application/json: schema: $ref: '#/components/schemas/ExternalEntityCreationRequest' responses: '201': description: Successfully created an external entity. content: application/json: schema: $ref: '#/components/schemas/ExternalEntity' examples: response: value: walletId: '212000' businessName: Circle Internet Financial Inc. businessUniqueIdentifier: '1234567890' identifierIssuingCountryCode: US complianceState: PENDING '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/NotAuthorized' '409': $ref: '#/components/responses/Conflict' security: - bearerAuth: [] components: schemas: ExternalEntityCreationRequest: type: object required: - businessName - businessUniqueIdentifier - identifierIssuingCountryCode - address properties: businessName: type: string description: The name of the business. example: Circle Internet Financial Inc. businessUniqueIdentifier: type: string description: >- The unique identifier of the business. For example, a company number or tax ID. example: '1234567890' identifierIssuingCountryCode: type: string description: >- The country code of the issuing authority. Formatted as a two-letter country code specified in ISO 3166-1 alpha-2. pattern: ^[A-Z]{2}$ example: US address: $ref: '#/components/schemas/InstitutionalAddress' ExternalEntity: type: object description: An external entity properties: walletId: $ref: '#/components/schemas/InstitutionalWalletId' businessName: type: string description: The name of the business. example: Circle Internet Financial Inc. businessUniqueIdentifier: type: string description: >- The unique identifier of the business. For example, a company number or tax ID. example: '1234567890' identifierIssuingCountryCode: type: string description: >- The country code of the issuing authority. Formatted as a two-letter country code specified in ISO 3166-1 alpha-2. pattern: ^[A-Z]{2}$ example: US complianceState: type: string description: The compliance status of the external entity. enum: - PENDING - ACCEPTED - REJECTED InstitutionalAddress: type: object required: - country - state - city - postalCode properties: country: type: string description: >- Country portion of the address. Formatted as a two-letter country code specified in ISO 3166-1 alpha-2. pattern: ^[A-Z]{2}$ example: US state: type: string description: >- State / county / province / region / district / emirate portion of the address. US and Canada use the two-letter code for the subdivision. example: MA city: type: string description: City portion of the address. example: Boston postcode: type: string description: >- Postal / ZIP code of the address. If there is no applicable postal code, set the value to `00000`. example: '01234' streetName: type: string description: Street name of the address. example: Main Street buildingNumber: type: string description: Street number of the address. example: '100' InstitutionalWalletId: type: string description: >- Unique system-generated identifier for the wallet of the institutional entity. example: '212000' responses: BadRequest: description: The request cannot be processed due to a client error. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' content: application/json: schema: type: object title: BadRequest required: - code - message properties: code: type: integer example: 400 message: type: string example: Something went wrong. example: code: 400 message: Bad request. examples: response: value: code: 400 message: Bad request. NotAuthorized: description: >- The request has not been applied because it lacks valid authentication credentials. headers: X-Request-Id: $ref: '#/components/headers/XRequestId' content: application/json: schema: type: object title: NotAuthorized required: - code - message properties: code: type: integer example: 400 message: type: string example: Something went wrong. example: code: 401 message: Malformed authorization. examples: response: value: code: 401 message: Malformed authorization. Conflict: description: >- The request has not been applied because it comes in conflict with another request (such as re-using an idempotencyKey for a different request). headers: X-Request-Id: $ref: '#/components/headers/XRequestId' content: application/json: schema: type: object title: Conflict required: - code - message properties: code: type: integer example: 400 message: type: string example: Something went wrong. example: code: 409 message: Conflicts with another request. examples: response: value: code: 409 message: Conflicts with another request. headers: XRequestId: description: >- Universally unique identifier (UUID v4) for the request. Helpful for identifying a request when communicating with Circle support. schema: type: string format: uuid example: 2adba88e-9d63-44bc-b975-9b6ae3440dde securitySchemes: bearerAuth: type: http scheme: bearer ````