> ## 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. # Save data for multiple sections in a single request > Accepts a JSON object keyed by section name. Each value is the same payload shape as PUT /sections/{sectionName}. Validation is atomic: all sections are validated before any data is saved, and if any section fails validation the entire request is rejected. Saves are sequential: after validation passes, sections are persisted one at a time. Array sections use upsert semantics: items with refId update existing entities, items without refId create new entities. Existing entities not included are preserved. The response data field is an object keyed by section name containing the saved data for each section. ## OpenAPI ````yaml openapi/partner-openapi.yaml patch /v1/onboarding/partner/applications/{applicationId}/data openapi: 3.1.0 info: description: > Partner-facing API for programmatic onboarding. Use these endpoints to create and manage onboarding applications on behalf of your customers, submit sections of data, upload supporting documents, and respond to Requests for Information (RFIs). ## Authentication All endpoints require a Bearer token obtained via the Circle key exchange. Include the token in the `Authorization: Bearer ` header. ## Idempotency All POST endpoints in this API require an `X-Idempotency-Key` header. Provide a client-generated UUID v4 with each POST request. If the same key is retried, the original response is returned without re-executing the operation. Omitting the header on a POST will result in a 400 error. This requirement covers the endpoints defined in this specification. Other partner APIs set their own idempotency rules; for example, creating a partner client (`POST /v1/partner/clients`, defined in the Customer Orchestration API) does not require the header. title: Circle Partner Onboarding API version: '2026-04-15' servers: - description: Production url: https://api.circle.com - description: Sandbox url: https://api-sandbox.circle.com security: - bearerAuth: [] paths: /v1/onboarding/partner/applications/{applicationId}/data: patch: tags: - Partner Applications summary: Save data for multiple sections in a single request description: >- Accepts a JSON object keyed by section name. Each value is the same payload shape as PUT /sections/{sectionName}. Validation is atomic: all sections are validated before any data is saved, and if any section fails validation the entire request is rejected. Saves are sequential: after validation passes, sections are persisted one at a time. Array sections use upsert semantics: items with refId update existing entities, items without refId create new entities. Existing entities not included are preserved. The response data field is an object keyed by section name containing the saved data for each section. operationId: bulkSave parameters: - description: Application UUID example: 550e8400-e29b-41d4-a716-446655440000 in: path name: applicationId required: true schema: type: string format: uuid - description: >- When true, emit array/object/number field values as native JSON nodes in the echoed response data. Defaults to false. in: query name: typedValues schema: type: boolean default: false requestBody: content: application/json: schema: type: object description: >- Section data keyed by section name — structure varies by template. Consult GET /{applicationId}/schema. description: >- JSON object keyed by section name. Each value matches the section's JSON Schema. responses: '200': content: application/json: schema: $ref: '#/components/schemas/SectionSaveResponse' description: All section statuses after save '400': description: Invalid request (unknown section, empty payload) '401': description: Authentication required '403': description: Insufficient permissions '404': description: Application not found '409': description: Application is not in an editable state '422': description: Validation error components: schemas: SectionSaveResponse: type: object properties: data: type: object description: >- Saved section field data — structure varies by application template. For single-section saves this is the section payload directly. For bulk saves this is an object keyed by section name. Retrieve the shape via GET /{applicationId}/schema. fieldsChanged: type: boolean sections: type: array items: $ref: '#/components/schemas/ApplicationSectionSummary' sectionsChanged: type: boolean ApplicationSectionSummary: type: object properties: sectionName: type: string status: type: string enum: - action_required - complete - incomplete - not_started securitySchemes: bearerAuth: bearerFormat: JWT description: Bearer token obtained via Circle key exchange scheme: bearer type: http ````