Install the MCP server

The skill is enough for most agents; install the server when you want tools instead of HTTP, rules that hold in every session without a skills directory, or an agent that can pay.

	Skill, one message	MCP server	Client library in code	`pay_x402`, server plus your wallet
Setup	tell your agent to read skill.md	one command or one config block (the skill does this for you where it can)	`npm install`, wrap your fetch	`paidfor-mcp wallet new`, fund a few USDC
Checks before paying	yes, over HTTP	yes, as a tool with structured results	yes, inside the call	yes
Rules persist	where the client has a skills directory	every session the server is attached, via instructions on initialize	in your code	same as the server
Never pays twice	by rule, the agent's discipline	by rule	enforced: intent ids and receipts	enforced
Caps and price checks	the agent reads them	the agent reads them	enforced: per-call cap, listed-price ratio, validators	enforced
Works in chat clients with no shell	rules for that conversation only	yes, as a connector	no	no
Outcomes reported back	only if the agent reports after paying	same, unless `pay_x402`	automatic, verified on-chain	automatic, verified on-chain
Session-start alerts for your allowlist	yes, from project notes	yes, via the `recent_changes` tool	no	yes
What it gives the index	demand, candidates (soon), agent-reported outcomes	the same, plus tool analytics	verified outcomes	verified outcomes

The server gives your agent check_x402_seller, which it calls before paying an x402 seller, list_reliable_sellers and recent_changes. No key, no account; it sends nothing but the URL being checked.

Tell your agent: install paidfor from https://paidfor.dev/install.md

Download paidfor.mcpb Add to Cursor Add to VS Code

Paste into Claude Code's agent

Install the paidfor MCP server in Claude Code. It needs no key and sends nothing but the URL being checked.
Run `claude mcp add --transport http --scope user paidfor https://mcp.paidfor.dev/mcp`.
Show me the diff before writing anything.
Start a new session (or run /mcp to reconnect) so the tools load.
Then call check_x402_seller with api-xpay.com and confirm the verdict is avoid.

Command

claude mcp add --transport http --scope user paidfor https://mcp.paidfor.dev/mcp

Start a new session (or run /mcp to reconnect) so the tools load. To check it works, ask for check_x402_seller on api-xpay.com: the verdict should be avoid.

Already paying from code?

Paste this into Claude Code or Cursor inside your project. It wraps your existing x402 calls with @paidfor/x402-safe-fetch, which checks the seller and caps the price before paying; the README has every option.

Migration prompt

Install @paidfor/x402-safe-fetch. Find every place this project calls an x402 seller (look for @x402/fetch, wrapFetchWithPayment, X-PAYMENT or PAYMENT-SIGNATURE headers). Wrap each with safeFetch using maxPerCallUsd 0.50, maxOverListedRatio 1.1 and refuseVerdicts ["avoid"], keep the wallet client as it is, add the receipts directory to .gitignore, show me the diff before committing, then run the project's existing tests.

Let your agent pay, safely

With a wallet configured, the stdio server (@paidfor/mcp@0.3.1 or later) adds pay_x402, which pays through @paidfor/x402-safe-fetch: it checks the seller first, refuses avoid sellers and quotes over 1.1x the listed price, caps each call (PAIDFOR_MAX_PER_CALL_USD, default 0.50) and each day (PAIDFOR_DAILY_CAP_USD, default 5), never pays twice for one intent, and reports the verified outcome to the index. Use a dedicated wallet holding a few dollars; the key stays on your machine and is never logged, returned or sent.

1. Make a wallet (writes ~/.paidfor/wallet.key, mode 600, prints the address)

npx -y @paidfor/mcp@0.3.1 wallet new

2. Fund it

Send a few USDC on Base to the printed address. x402 payments on Base are gasless for the buyer, no ETH needed.

3. Set the env in the client config (stdio, not the hosted URL)

{
  "mcpServers": {
    "paidfor": {
      "command": "npx",
      "args": [
        "-y",
        "@paidfor/mcp@0.3.1"
      ],
      "env": {
        "PAIDFOR_WALLET_KEY_FILE": "/Users/you/.paidfor/wallet.key",
        "PAIDFOR_MAX_PER_CALL_USD": "0.50",
        "PAIDFOR_DAILY_CAP_USD": "5"
      }
    }
  }
}

4. Verify

Restart the client and ask the agent to call wallet_status: it shows the address, the USDC balance on Base and the limits, never the key.

The hosted server cannot pay, by design: it never holds a key, so it only has the two read tools.

For agents: /install.md (also at /llms-install.md). Endpoints and the response contract: API and MCP.