x402 and MCP: paid tools for AI agents
MCP is how an agent discovers and invokes tools; x402 is how it pays for the ones that aren't free. Together they let an agent find a paid tool, call it, and settle a few cents per use — no signup, no API key.
What MCP does, What x402 adds, How they compose
What MCP does
The Model Context Protocol (MCP) is how an agent discovers and invokes tools. An MCP server advertises a set of tools with typed inputs; an MCP client — Claude Desktop, Cursor, or your own agent framework — lists them and calls them. MCP standardizes the tool interface, but it says nothing about how a paid tool gets paid.
What x402 adds
x402 is the payment layer MCP lacks. When a tool isn't free, the server can answer with HTTP 402 and a payment challenge; the caller settles a small USDC-on-Base payment and retries. Together they cover the whole loop: MCP for discovery and invocation, x402 for per-call settlement — no signup or API key in between.
How they compose
An MCP server exposes a tool that proxies to an x402-metered HTTP endpoint. The agent calls the MCP tool; the proxy forwards the request and returns the 402 challenge; the agent's x402 wallet signs the payment and the call completes, returning the result through MCP as usual. The agent gets a normal MCP tool that happens to cost a few cents to run.
Calling a paid MCP tool in practice
Point your MCP client at the Hermes Plant MCP server and the finance and quant tools appear automatically — cashflowlens_analyze, waterfall_distribute, options_price, bond_analyze, and more. Each call returns a 402 your client settles with an x402 wallet. There is nothing to provision: discover the tool, call it, pay per use.
Where to start
Add the Hermes Plant MCP server to your agent, fund a small USDC-on-Base balance, and call a finance tool. Read the x402 explainer for the payment mechanics, and the agent services pages for each endpoint's inputs, price, and example.
FAQ
Does MCP handle payments?
No. MCP standardizes how tools are discovered and called, not how they are paid for. x402 fills that gap: a paid MCP tool can return an HTTP 402 challenge that the agent's x402 client settles in USDC, then retries to get the result.
How does an agent pay for an MCP tool?
When an MCP tool proxies to an x402-metered endpoint, the call returns a 402 payment challenge. The agent's x402 wallet signs a small USDC-on-Base payment and the call completes — no API key or subscription, just a few cents per call.