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Guide

Shield crypto spend

Give the agent a wallet that holds only run money, cap each payment before any signature, and learn the x402 buyer handshake. Educational. Agent Lane does not hold keys or run a facilitator.

Page dated 12 September 2026

Not legal, tax, or investment advice. Agent Lane is a publisher. We do not place trades, custody assets, or operate your agents. Confirm every step on the official product page before you fund a run.

What this page is

A buyer-side checklist for operators who let Cursor or Grok pay for HTTP resources, MCP tools, or other machine-priced endpoints. It is not a wallet, a custodian, an exchange account, or a payment product.

If you meant crypto orders inside a Robinhood Agentic brokerage account, that is a different lane — see shield brokerage spend. This page is about keys you control and payments that settle on-chain.

Dedicated wallet

Do not point an agent at the wallet that holds savings, payroll, or the keys you would mourn. Open (or generate) a wallet whose only job is agent spend. Fund it with the ceiling for a defined window — a day, a week, a single project — and refill it yourself after you look at the receipts.

  • One agent identity, one spend wallet. Do not share that wallet across housemates, contractors, or a second operator’s Grok account.
  • Keep the seed phrase and private key off the machine the agent runs on when you can. A signing service or a hardware path you approve is a different design than a raw key in .env.
  • If the key must live on the box, it still must not live in chat, in a pasted prompt, in a repo, or in a screenshot.
  • Empty the wallet when the project ends. An unused key with a leftover balance is still a live spend path.

A key in agent context is a key the next prompt, log, shared user, or leaked transcript can spend. Treat “the model needed the key to sign” as a last resort, not a default.

Per-run caps you enforce

Sellers quote a price. That quote is not your budget. The cap lives inyour wrapper, before any signature:

  1. Read the amount and asset out of the 402 / payment-required payload.
  2. Compare it to a max you set for this run (and, separately, a cumulative max for the day).
  3. Refuse and stop if the quote is over the cap, on the wrong asset, or on a network you did not allow.
  4. Allowlist destinations. An unknown resource URL is a no, even if the price is a cent.
  5. Log the quote, the decision, and the receipt. A run without a receipt is an unclosed loop.

Some buyer SDKs advertise spend controls (per-payment caps, cumulative caps, allowlists). Use them if you use that SDK — and still keep a cap in a layer you understand well enough to read. A library default is not a policy you wrote.

x402 buyer basics

x402 is an open payment protocol that uses HTTP 402 Payment Requiredso a client can pay for a resource without opening a merchant account. Coinbase and the x402 docs describe the handshake. Header names and SDK wrappers have already moved once; confirm the current buyer quickstart before you write a client.

  1. The agent requests a URL or tool.
  2. If payment is required, the server answers 402 with machine-readable terms: amount, asset, network, pay-to address, scheme.
  3. Your wrapper checks those terms against the cap and allowlist.
  4. If they pass, a local signer builds a payment payload. In common USDC flows this is an authorization the agent signs; a facilitator may submit the on-chain transfer and pay gas.
  5. The client retries the same request with the payment proof. A successful response includes a settlement receipt.

The important operator facts: no money should move until the retry you approved; the seller’s 402 is a quote, not a command; and “gasless for the agent” does not mean “free” or “uncapped.” The spend is the USDC (or other asset) you authorized.

Automatic pay-on-402 wrappers are convenient and easy to leave wide open. If your client will pay without asking, the only real brakes are the wallet balance and the caps in your code. Set both before the first live call.

A first live path (still DIY)

Official buyer docs start on a test network (often Base Sepolia plus test USDC) with a published protected URL. Do that before mainnet:

  1. Install the current @x402/fetch (or the Python / Go buyer package) from the official quickstart — package names move; copy them from the docs, not from memory.
  2. Point the signer at the dedicated spend wallet, not at a vault wallet.
  3. Hard-code a tiny max amount and a single allowlisted URL.
  4. Complete one paid call. Read the receipt. Then decide whether a second URL is worth opening.

Agent Lane does not ship a wallet, a facilitator, or a hosted buyer. If a later page adds a software link, it will be dated and marked unpaid or paid in the same sentence as the link.

What Agent Lane does not do here

  • We do not take custody, run a hot wallet, or settle payments.
  • We do not tell you which chain, stablecoin, or facilitator to use.
  • We do not publish a funded “agent buyer” you can point at production APIs.

Official product links

Sources

x402 buyer quickstart,docs.x402.org, and Coinbase Developer docs on how x402 works, read 12 September 2026. Protocol header names in current transport drafts include payment-required and payment-signature fields; older write-ups used X-PAYMENT. Use the live spec, not this paragraph, when you implement.