{"id":"crypto","title":"USDC pay-per-call client","markdown":"# USDC client for AI agents\n\nUse real USDC on Base mainnet to pay for individual Agent Utilities calls without a $5 Stripe pack. The Node.js 22+ ES module includes Circle's signing SDK and our required request-binding signature; no npm install is needed. Importing it makes no network request or payment.\n\nDownloads:\n- [Client module](/downloads/agent-utilities-crypto.mjs)\n- [SHA-256 checksum](/downloads/agent-utilities-crypto.mjs.sha256)\n- [Runnable GTIN example](/downloads/crypto-example.mjs)\n- [Example checksum](/downloads/crypto-example.mjs.sha256)\n- [License notices](/downloads/CRYPTO-CLIENT-NOTICES.txt)\n\n## Preview without funds\n\nDownload both modules into the same directory, along with their checksum files. Verify and preview:\n\n```sh\nshasum -a 256 -c agent-utilities-crypto.mjs.sha256\nshasum -a 256 -c crypto-example.mjs.sha256\nnode crypto-example.mjs --preview\n```\n\nPreview is offline. It displays the fixed GTIN input, Base mainnet network and 300-micro-USDC ceiling (0.0003 USDC). No wallet, signature, deposit or API call is needed.\n\n## Prepare and send a real call\n\nUse a separately approved paying wallet with a funded Circle Gateway balance. It must differ from the merchant receiving wallet. Testnet tokens cannot pay mainnet calls. Deposits and withdrawals can incur fees; initial Base deposits can take time. The browser [wallet workspace](/wallet#wallet) offers funding controls. The client does not deposit, bridge or withdraw money.\n\nRead [/wallet-config](/wallet-config) and independently approve its receiving address. Set these variables through your private secret manager or local environment, never in source, a URL or a shared transcript:\n\n- `BUYER_PRIVATE_KEY`: paying EOA wallet private key; only preparation uses it.\n- `PAYMENT_NETWORK`: explicitly `eip155:8453` for this example.\n- `PAYMENT_RECIPIENT`: the receiving address you have approved.\n\n```sh\nnode crypto-example.mjs --prepare ./my-private-call.json\n# Review your intended operation. The next command authorizes submission:\nnode crypto-example.mjs --send ./my-private-call.json\n```\n\nPreparation obtains a quote and signs at most 0.0003 USDC for `commerce.gtin-validate` with input `{\"code\":\"036000291452\"}`. It writes the signed request to a new file with owner-only permissions and flushes it before returning. It never overwrites an existing file and does not submit settlement. The state file contains a spend authorization and input: keep it private and out of source control.\n\nSend within five minutes of preparation. `--send` needs no private key; it sends the saved request once. It may spend real USDC. After a lost response or an uncertain settlement, repeat **the same `--send` command with the same file**. Recovery lasts ten minutes from the server's first claim. Never prepare a fresh request to retry an uncertain payment, and do not edit the file. If preparation failed and left an empty file, no payment was submitted by that command; inspect the failure before choosing a fresh operation path.\n\nThe example deliberately separates signing and sending and performs no automatic reauthorization. Successful output includes a result, Gateway receipt and recovery deadline. Acceptance is not final on-chain confirmation. A failed network response is not proof that no payment occurred.\n\n## Import into your own agent\n\n```js\nimport { prepareCall, sendPrepared, privateKeyToAccount } from './agent-utilities-crypto.mjs';\n```\n\n`prepareCall({url, body, account, maxMicroUsdc, expectedRecipient, expectedNetwork})` requests one quote, checks the ceiling, recipient, network, token and Gateway contract, then creates the two required signatures. `account` may be `privateKeyToAccount(...)` or your signing wallet adapter with `address`, `signTypedData` and `signMessage`. Only EOA signing is supported by this integration. Network may be `eip155:8453` (Base mainnet) or `eip155:84532` (separate test deployment); never infer it from an untrusted quote.\n\nThe returned object contains `url`, `body`, `headers` and `quoteExpiresAt`. Persist it privately before the first `sendPrepared(prepared)` if your process may restart. That function sends the object unchanged, does not sign again, does not follow redirects and returns a Fetch Response. Set an independent ceiling for each new logical operation and enforce an overall budget in your agent. A per-call ceiling is not a session spending limit.\n\nRead the chosen tool's schema from [/v1/tools](/v1/tools). An ordinary x402 client does not automatically support our extra input-binding signature. The downloadable module does. Existing MCP and Python adapters continue to use Stripe credits; importing this module does not change their payment method.\n"}