CRA AGENT

@cra-agent/mcp

An MCP server that lets an AI agent pay for an API call. The agent calls one tool, the rail reads the x402 price, checks a spending policy, pays in USDC on Arc through Circle Gateway with no gas for the buyer, and keeps the receipt.

The model never sees the key, and it cannot raise its own limit: both are read from the environment before the conversation starts.

Install

npm i -g @cra-agent/mcp

Set it up in one command

cra-agent init --client claude-desktop

Creates the agent's key in ~/.cra-agent/agent.key (readable only by you, never overwritten), checks the limits, writes the entry into the client's config file with a copy of the old one, and prints the address to fund. --client is claude-desktop, cursor, claude-code or terminal; --policy, --network, --key-file and --dry-run do what they say. CRA Factory writes the command for you from four questions.

Or by hand, from any MCP client

{ "mcpServers": { "cra-agent": {
    "command": "cra-agent-mcp",
    "env": {
      "CRA_NETWORK": "arc",
      "CRA_KEY_FILE": "/path/to/agent.key",
      "CRA_POLICY": "daily=5,per_seller=0.5,per_payment=0.05"
    }
} } }

CRA_KEY_FILE points at a file holding the private key, chmod 600. Never put a key in a prompt.

Tools

Tool	What it does
arc_search	Finds what can be bought on Arc from a few words ("bitcoin price", "web search"): CRA AGENT's own data, the CRA market, and the endpoints Circle's x402 catalogue lists as payable on Arc (Exa, Goldsky, BlockRun and others). Each result: the method and the URL with example parameters, where each parameter goes (query, path or JSON body), the price, the seller, who listed it, and whether your policy allows paying it now. Free.
arc_quote	Reads the price of a URL and says whether the policy would allow it. Pays nothing. For a POST, pass the body the payment will carry: some sellers check it before they name a price.
arc_pay	Pays for the URL and returns the response with a receipt. With lightning: true it pays in bitcoin over Lightning when the seller's 402 offers it (x402 exact on lnbtc), from the wallet in CRA_NWC_PAY_FILE, under the same limits in dollars. Limits are checked on what the 402 asks at pay time, before anything is signed. maxUsdc adds a ceiling for that one call: pass the price arc_search listed, and a seller who raised it since is refused even inside your limits.
arc_balance	Wallet and Circle Gateway balances.
arc_deposit	Moves wallet USDC into the Gateway balance. Needed once before the first payment.
arc_ledger	Every attempt: quoted, rejected, signed, settled, failed.
arc_proof	Matches settled payments to the on-chain transfer that carried them.
arc_verify_receipt	Checks a signed receipt from another agent: who signed it, and whether the payment fitted the limits it states.
arc_policy	Shows the limits in force.
arc_job_*	ERC-8183 escrow jobs. Testnet only until the contract is deployed on Arc mainnet.

An agent that pays for its own thinking

cra-agent think "<task>" runs a small autonomous agent whose brain is a pay-per-call LLM on Arc: BlockRun's chat completions, found in the bazaar, Claude Haiku 4.5 by default. Every thought is a paid call, and so is every tool the brain asks for: it searches the bazaar for free, then buys what it needs at the listed price. There is no API key anywhere, only the agent's wallet. The session budget (--budget, default $0.10) and the spending policy cover thinking and tools alike, a thought is capped with --ceiling (default $0.01), and the brain can only buy a URL that one of its searches returned. It prints each step with its cost and ends with the bill: so much for thinking, so much for tools. A short task costs a few cents: the run on cra-agent.tech/think that found when Arc mainnet went live and who validates it cost $0.023648, four thoughts and one web search from Exa.

It also knows a few free public APIs, called without paying and shown as such: DexScreener's pairs, boosted tokens and new token profiles, digested to what answers questions (pairs by 24-hour volume). --tools <file> keeps it to a list of URL prefixes: anything else is never shown to it, so never bought.

With --record and a DATABASE_URL, the run is kept in Postgres as it happens, step by step, which is how the page shows it live and replays it after. --questions <file> picks the question when none is given, which is how our server runs it on a timer: the file combines templates (What is the price of {coin} right now?) with lists (@coin = bitcoin (BTC) | ether (ETH)), and a recorded run never repeats one of the last hundred questions.

The same agent can be hired by anyone, over x402 upto: GET https://api.cra-agent.tech/v1/upto/think?task=… asks you to sign for up to $0.10 and charges what the run spent plus $0.005. arc_pay and cra-agent pay pay routes like this one: your policy is checked against the ceiling, since all of it could be taken, and your ledger keeps what was. The default policy allows $0.05 a payment, so give this one more with per_payment=0.10.

Fund the agent from Base or Solana

Paying on Arc takes USDC in Circle Gateway on Arc, and most agents hold theirs on Base or Solana. One command brings it over and deposits it:

cra-agent fund 5 --from base                                    # from this agent's own wallet on Base, same key and address
cra-agent fund 5 --from solana --solana-key-file ~/sol.json     # from a Solana wallet: our hex seed or solana-keygen's JSON
cra-agent fund 5 --from base --dry-run                          # everything checked, nothing signed

It asks Eco for a route, and checks the quote before signing anything, from the transaction's own calldata: a CCTP burn of exactly that amount to Arc's domain, minting to this agent, a fee under the cap (--max-fee, default 0.5% or $0.01), the refund to the same wallet. From Base, the vault the USDC goes into must be the one Eco's Portal derives for that intent. It then waits for the USDC on Arc, usually seconds, and deposits it into Gateway, leaving $0.01 in the wallet for Arc's gas (--keep, or --no-deposit to keep it all in the wallet). From Base the wallet needs a little ETH for two transactions, about a cent; from Solana, a little SOL. The model has no tool for this: moving money between chains is the owner's call, from a terminal.

The same thing from a terminal

cra-agent find bitcoin price    # what is for sale on Arc; needs no key (in a browser: cra-agent.tech/bazaar)
cra-agent balance
cra-agent quote https://api.cra-agent.tech/v1/paid/rpc/health
cra-agent quote https://api.exa.ai/search --body '{"query":"x402 on Arc"}'           # the price of a POST, with its body
cra-agent fund 5 --from base   # USDC from Base to this agent on Arc, into Gateway
cra-agent deposit 1
cra-agent withdraw 1            # Gateway balance back to the wallet; how a seller collects
cra-agent pay   https://api.cra-agent.tech/v1/paid/rpc/health
cra-agent pay   https://api.exa.ai/search 0.007 --body '{"query":"x402 on Arc"}'   # a POST, refused above the listed price
cra-agent think "What is x402, in two sentences?" --budget 0.10              # an agent that pays for its own thinking
cra-agent proof
cra-agent verify receipt.json      # needs no key and no network
cra-agent pq-key ~/.cra-agent/pq.key           # a post-quantum key for receipts; prints only its public half
cra-agent verify receipt.json --require-pq --on-arc   # the second signature too, and Arc's own verdict on it

Every receipt carries the limits the payment passed under and is signed with the agent's key, so someone who was not there can check it. The signature proves the agent issued the statement and nobody changed it; the settlement on chain is the independent half.

Environment

Variable	Meaning
CRA_NETWORK	arc (mainnet) or arcTestnet. Default arcTestnet.
CRA_KEY_FILE / CRA_PRIVATE_KEY	The agent's key. Prefer the file.
CRA_POLICY	daily=5,per_seller=0.5,per_payment=0.05,rate=120/60s,allow=a.com|b.com,deny=c.com
CRA_RPC_URL	Optional, one or several separated by commas, in priority order. Tried before the public Arc endpoints.
CRA_RPC_STRICT	1 to never fall back to a public endpoint.
CRA_BASE_RPC_URL / SOLANA_RPC_URL	Optional, for fund: the Base and Solana endpoints. Public ones by default.
DATABASE_URL	Optional Postgres for the ledger. Without it the ledger lives in memory.
CRA_PQ_KEY_FILE	Optional, the file cra-agent pq-key made. Every receipt is then signed a second time with SLH-DSA-SHA2-128s, the post-quantum scheme Arc verifies on chain. It covers the receipt, not the payment, and adds about a second to each one.

Two things worth knowing. A payment is settled only after the seller's handler succeeds, so a failing endpoint costs nothing: https://api.cra-agent.tech/v1/paid/selftest/fail always answers 500 so you can check. And identity=required pays only sellers with an ERC-8004 identity on Arc: the address that gets paid must own an agent in the registry, or be the wallet an agent declared for payments. It proves an identity exists, not that the seller is honest; registering costs only gas.

Part of CRA AGENT

Payments for AI agents on Arc, Circle's USDC-native L1. Site: cra-agent.tech · Source: github.com/giupy997/arcagentx402 · MIT