Do Claude or ChatGPT pay for MCP tools?
Not on their own. Claude and ChatGPT can call MCP tools, but neither carries a wallet, so neither pays for a tool by itself.
How a paid MCP tool call works
Charging for an MCP tool call runs the same loop as x402 over HTTP, carried in MCP's wire format. The client calls the tool with no payment attached. The server answers with isError: true and a PaymentRequired payload, MCP's equivalent of an HTTP 402. The client builds a payment, retries the same call with it attached at _meta['x402/payment'], and the server verifies and settles the payment and returns the real result with settlement details at _meta['x402/payment-response'].
Who signs the payment
The payment is signed by a wallet on the client side. Coinbase's documentation pairs the @x402/mcp client wrapper with a CDP-managed wallet; the x402 documentation's MCP guide uses an Ethereum wallet funded with USDC on Base, or a Solana wallet. A chat product without such a wrapper and wallet receives the PaymentRequired result and stops there: the tool returns its price, not its output.
Spending limits live in the same client layer. The CDP SDK's x402 client, for example, exposes spend controls (a SpendTracker and a SpendControlError are part of its public interface), so the operator decides how much an agent may pay per call and in total.
What this means if you sell a paid MCP tool
The buyers are agents and scripts whose operators gave them a wallet and a budget, not people typing in a chat window. Those agents read the tool's description as task input, so a description that states what the tool returns, what it costs and on which network, in plain words, is what they can act on.
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The pages below go deeper on this question.
Sources and observed evidence
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Publish an x402 API profile with a readiness report and badge
Prepare your x402 API for agent discovery: validate free, inspect readiness evidence, then publish an Ontario service profile for 0.50 USDC only when you need it.
MCP Registry, Smithery or Bazaar: build the agent purchase path
Separate MCP installation from paid API discovery. Give agents a callable tool, free preflight, explicit payment requirements and evidence of fulfilled output.
Can x402 payments be refunded?
An x402 payment is a USDC transfer that is final once it settles, so a refund is a voluntary new transfer and the real protection is a seller that settles after the result exists.
How big is the x402 market?
Coinbase's Bazaar index lists tens of thousands of paid endpoints, but most show one or two payers in 30 days, and repeat demand sits in a few categories.
Are cheaper x402 APIs worse?
Not necessarily; price rarely decides which x402 API agents use, as a reseller that charges more than the original search API and gets more calls shows.
Which networks does x402 support?
x402 is network-agnostic; Coinbase's facilitator settles on Base, Solana, Polygon, Arbitrum, Monad and World, and most paid traffic today is USDC on Base.
How do I get my API discovered by AI agents?
Agents search indexes rather than browse websites, so an API is found through Coinbase's Bazaar, x402scan and directories, and through a description that names the task.
How do I know an x402 endpoint is legit?
Three observable checks show whether an unknown x402 endpoint is live, priced as listed and used by repeat buyers; Ontario's finder runs them for 0.005 USDC.