> ## 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. # Quickstart: Assess the risk of wallet addresses Transaction Screening allows you to programmatically assess the risk of wallet addresses when sending digital assets using Circle Wallets. This guide walks you through setup, integration, and testing using Circle's Compliance Engine. This guide applies specifically to the [standalone screening](/wallets/compliance-engine/tx-screening#standalone-screening) mode, where blockchain addresses are screened independently of transaction flows. Compliance Engine on both testnet and mainnet is only available for eligible customers. Contact Circle through the [Compliance Engine request form](https://www.circle.com/wallets/compliance-engine/#get-in-touch) to get access. ## Prerequisites Before you begin, make sure you have the following: * A Circle Developer Account * An API key with appropriate access to [Compliance Engine](https://console.circle.com/compliance) * [Node.js](https://nodejs.org/en/download) installed, or an API tool like Postman or cURL * [Axios](https://axios-http.com/) installed, if using Node.js ## Steps Follow the steps below to screen an address: ### 1. Generate a test address To simulate a real screening scenario, visit [vanity-eth.tk](https://vanity-eth.tk) to generate a test Ethereum wallet address ending in `9999`: For example, `0x7fb49965753A9eC3646fd5d004ee5AeD6Cc89999`. The `9999` suffix triggers Circle's sanctions blocklist in the screening API. ### 2. Screen the wallet address explicitly using Circle's API Submit a `POST` request to the screening API using Node.js: ```javascript JavaScript theme={null} import axios from "axios"; const options = { method: "POST", url: "https://api.circle.com/v1/w3s/compliance/screening/addresses", headers: { Authorization: "Bearer ", "Content-Type": "application/json", }, data: { idempotencyKey: "44bd2d89-9461-4502-84ba-550c9e278db7", // unique-idempotency-key address: "0x7fb49965753A9eC3646fd5d004ee5AeD6Cc89999", chain: "ETH-SEPOLIA", }, }; axios .request(options) .then(function (response) { console.log(response.data); }) .catch(function (error) { console.error(error); }); ``` **Note:** You must replace the `` above with your actual Circle API key. ### 3. Review the screening response If the address is flagged, the response returns a `DENIED` result with some actionable compliance recommendations: ```json JSON theme={null} { "result": "DENIED", "decision": { "ruleName": "Circle's Sanctions Blocklist", "actions": ["FREEZE_WALLET", "DENY", "REVIEW"], "reasons": [ { "source": "ADDRESS", "sourceValue": "0x7fb49965753A9eC3646fd5d004ee5AeD6Cc89999", "riskScore": "BLOCKLIST", "riskCategories": ["SANCTIONS"], "type": "OWNERSHIP" } ], "screeningDate": "2025-03-29T01:59:02Z" }, "address": "0x7fb49965753A9eC3646fd5d004ee5AeD6Cc89999", "chain": "ETH-SEPOLIA" } ``` ### 4. Evaluate screening recommendations If the screening result is `DENIED`, you can take the following actions based on the recommendations provided: * **Block** the wallet from transaction activity (based on the `DENY` recommendation) * **Flag** the wallet for manual review (based on the `REVIEW` recommendation) * **Freeze** the wallet (based on the `FREEZE_WALLET` recommendation) You can **block** or **freeze** the wallet from the [Compliance Engine > Alerts](https://console.circle.com/compliance/alerts/screening) page in the Developer Console. For more details, see the [Alerts Management](/wallets/compliance-engine/tx-screening-alert-management) documentation. ## Automate rules based on screening outcomes You can integrate [actions and alerts](/wallets/compliance-engine/tx-screening-rule-management) into the transaction logic of your application: ```javascript JavaScript theme={null} if (response.data.result === "DENIED") { const ruleName = response.data.decision.ruleName; const actions = response.data.decision.actions; console.log("Screening result: DENIED by Rule: " + ruleName); if (actions.includes("DENY")) { console.log("Recommended action: DENY — block transactions on wallet"); } if (actions.includes("REVIEW")) { console.log("Recommended action: REVIEW — flag wallet for manual review"); } if (actions.includes("FREEZE_WALLET")) { console.log("Recommended action: FREEZE_WALLET — freeze wallet activity"); } } ``` You can also query additional fields such as `riskCategories`, `ruleName`, and `type` to make compliance decisions tailored to your business needs. For more information about these fields, refer to their descriptions in the response object of the [Screen a blockchain address](/api-reference/wallets/compliance/screen-address) API endpoint. ## Testing with simulated risk categories You can use specific suffixes in test addresses to simulate different risk scenarios: | Suffix | Simulated Rule Triggered | | - | - | | `9999` | Circle's Sanctions Blocklist | | `8888` | Frozen User Wallet | | `7777` | Custom Blocklist Rule | | `8999` | Severe Sanctions Risk (Owner) | | `8899` | Severe Terrorist Financing (Owner) | | `8889` | Severe CSAM Risk (Owner) | | `7779` | Severe Illicit Behavior (Owner) | | `7666` | High Illicit Behavior Risk (Owner) | | `7766` | High Gambling Risk (Owner) | **Test suffixes** are useful in pre-production environments for validation of custom rule enforcement and behavior.