AI agents can't hold ETH for gas. They shouldn't have to. Here's how to build a payment system where agents sign typed data and never touch gas or funds.<\/p>\n\n
Your AI agent needs to pay for an API, buy data, or settle a trade. Traditional approach: give it a wallet with ETH + USDC. But then you're managing gas balances, handling failed transactions, and praying the agent doesn't get drained.<\/p>\n\n
Instead of executing transactions, agents sign intents<\/em> - structured messages that say \"I want to pay X to Y.\" A relayer picks up the intent, validates it against spending policies, and submits the on-chain transaction.<\/p>\n\n The agent never needs ETH. Never submits a transaction. Never holds funds.<\/p>\n\n The SDK handles:<\/p>\n\n The relayer checks:<\/p>\n\n Only after all checks pass does it call the vault contract.<\/p>\n\n The on-chain \n \n \n Step 1: Define the intent structure\n<\/h3>\n\n\n\n
struct PaymentIntent {\n address bot; \/\/ The agent's address\n address to; \/\/ Payment recipient\n address token; \/\/ ERC-20 token (e.g. USDC)\n uint256 amount; \/\/ Amount in token decimals\n uint256 deadline; \/\/ Expiry timestamp\n bytes32 ref; \/\/ Reference hash (memo, invoice ID, etc.)\n}\n<\/code><\/pre>\n\n<\/div>\n\n\n\n\n \n \n Step 2: Agent signs the intent\n<\/h3>\n\n\n\n
import<\/span> {<\/span> AxonClient<\/span> }<\/span> from<\/span> '<\/span>@axonfi\/sdk<\/span>'<\/span>;<\/span>\n\nconst<\/span> axon<\/span> =<\/span> new<\/span> AxonClient<\/span>({<\/span>\n relayerUrl<\/span>:<\/span> '<\/span>https:\/\/relay.axonfi.xyz<\/span>'<\/span>,<\/span>\n botPrivateKey<\/span>:<\/span> process<\/span>.<\/span>env<\/span>.<\/span>BOT_PRIVATE_KEY<\/span>,<\/span>\n vaultAddress<\/span>:<\/span> '<\/span>0xYourVault<\/span>'<\/span>,<\/span>\n chainId<\/span>:<\/span> 8453<\/span>,<\/span>\n});<\/span>\n\n\/\/ Signs EIP-712 typed data + sends to relayer<\/span>\nconst<\/span> {<\/span> txHash<\/span> }<\/span> =<\/span> await<\/span> axon<\/span>.<\/span>pay<\/span>({<\/span>\n to<\/span>:<\/span> recipientAddress<\/span>,<\/span>\n amount<\/span>:<\/span> '<\/span>10.00<\/span>'<\/span>,<\/span> \/\/ 10 USDC<\/span>\n memo<\/span>:<\/span> '<\/span>Monthly API subscription<\/span>'<\/span>,<\/span>\n});<\/span>\n<\/code><\/pre>\n\n<\/div>\n\n\n\n\n
\n \n \n Step 3: Relayer validates and executes\n<\/h3>\n\n
\n
\n \n \n Step 4: Vault enforces on-chain\n<\/h3>\n\n\n\n
function executePayment(\n PaymentIntent calldata intent,\n bytes calldata signature\n) external onlyRelayer {\n require(bots[intent.bot].isActive, \"Bot not active\");\n require(block.timestamp <= intent.deadline, \"Expired\");\n require(intent.amount <= bots[intent.bot].maxPerTxAmount, \"Over limit\");\n\n \/\/ Verify EIP-712 signature\n bytes32 digest = _hashTypedDataV4(keccak256(abi.encode(...)));\n require(ECDSA.recover(digest, signature) == intent.bot, \"Bad sig\");\n\n \/\/ Transfer\n IERC20(intent.token).transfer(intent.to, intent.amount);\n}\n<\/code><\/pre>\n\n<\/div>\n\n\n\nmaxPerTxAmount<\/code> is the hard ceiling. Even if the relayer is compromised, the contract enforces per-bot limits.<\/p>\n\n\n \n \n Python version\n<\/h2>\n\n\n\n
from<\/span> axonfi<\/span> import<\/span> AxonClient<\/span>\n\naxon<\/span> =<\/span> AxonClient<\/span>(<\/span>\n relayer_url<\/span>=<\/span>\"<\/span>https:\/\/relay.axonfi.xyz<\/span>\"<\/span>,<\/span>\n bot_private_key<\/span>=<\/span>\"<\/span>0x...<\/span>\"<\/span>,<\/span>\n vault_address<\/span>=<\/span>\"<\/span>0x...<\/span>\"<\/span>,<\/span>\n chain_id<\/span>=<\/span>8453<\/span>,<\/span>\n)<\/span>\n\nresult<\/span> =<\/span> axon<\/span>.<\/span>pay<\/span>(<\/span>\n to<\/span>=<\/span>\"<\/span>0xrecipient<\/span>\"<\/span>,<\/span>\n amount<\/span>=<\/span>\"<\/span>5.00<\/span>\"<\/span>,<\/span>\n memo<\/span>=<\/span>\"<\/span>Data purchase<\/span>\"<\/span>,<\/span>\n)<\/span>\nprint<\/span>(<\/span>result<\/span>[<\/span>\"<\/span>txHash<\/span>\"<\/span>])<\/span>\n<\/code><\/pre>\n\n<\/div>\n\n\n\n\n \n \n LangChain integration\n<\/h2>\n\n\n\n
from<\/span> langchain_axon<\/span> import<\/span> AxonToolkit<\/span>\n\ntoolkit<\/span> =<\/span> AxonToolkit<\/span>(<\/span>\n relayer_url<\/span>=<\/span>\"<\/span>https:\/\/relay.axonfi.xyz<\/span>\"<\/span>,<\/span>\n bot_private_key<\/span>=<\/span>\"<\/span>0x...<\/span>\"<\/span>,<\/span>\n vault_address<\/span>=<\/span>\"<\/span>0x...<\/span>\"<\/span>,<\/span>\n chain_id<\/span>=<\/span>8453<\/span>,<\/span>\n)<\/span>\n\ntools<\/span> =<\/span> toolkit<\/span>.<\/span>get_tools<\/span>()<\/span>\n# Gives your agent: pay, swap, execute_protocol, get_balance, get_vault_value\n<\/span><\/code><\/pre>\n\n<\/div>\n\n\n\n\n \n \n Why this matters for agent builders\n<\/h2>\n\n
\n
\n \n \n Get started\n<\/h2>\n\n\n\n
npm install<\/span> @axonfi\/sdk\n# or<\/span>\npip install <\/span>axonfi\n<\/code><\/pre>\n\n<\/div>\n\n\n\n