Payments (x402)

Go Micro can require a payment before a tool runs, using x402 — the open HTTP 402 Payment Required standard for stablecoin payments, designed for AI agents and onchain APIs. It lets every Go Micro endpoint, already exposed as an AI-callable tool, become a paid tool: a service answers a call with 402 and payment requirements, the client pays and retries, and the gateway verifies the payment before serving.

Payments are opt-in and dependency-light. Go Micro carries no chain or crypto code — it speaks the protocol and delegates verification and settlement to a pluggable facilitator (Coinbase CDP, Alchemy, or self-hosted), so Base and Solana are just different facilitators behind one interface.

The wrapper

The core is HTTP middleware in go-micro.dev/v5/wrapper/x402:

import "go-micro.dev/v5/wrapper/x402"

pay := x402.Middleware(x402.Config{
    PayTo:          "0xYourAddress",            // where payments go (required)
    Network:        "base",                     // or "solana", ...
    Amount:         "10000",                    // smallest units, e.g. 0.01 USDC
    FacilitatorURL: "https://facilitator.example",
})
mux.Handle("/paid", pay(handler))

A request with no X-PAYMENT header gets a 402 with the requirements; once a payment verifies through the facilitator, the request is served (with settlement details on the X-PAYMENT-RESPONSE header).

Pluggable facilitator

Config.Facilitator is an interface; the default is an HTTPFacilitator pointed at FacilitatorURL. Implement your own to target any chain or hosted service:

type Facilitator interface {
    Verify(ctx context.Context, payment string, req Requirements) (Result, error)
}

At the MCP gateway

Because every endpoint is already an MCP tool, the gateway is where you charge. Payments are wired into both micro mcp serve and the standalone micro-mcp-gateway, gated on /mcp/call (listing tools and health stay free), and off unless you set a pay-to address.

micro mcp serve --address :3000 \
    --x402-pay-to 0xYourAddress \
    --x402-network solana \
    --x402-amount 10000 \
    --x402-facilitator https://facilitator.example

Per-tool amounts

Different tools can cost different amounts. Pricing is an operator concern — the payTo address is the operator’s, and amounts change without redeploying anyone’s service — so it’s configured at the gateway with a file, the same way per-tool scopes and rate limits are. Point the gateway at an x402 config:

micro mcp serve --address :3000 --x402-config x402.json

{
  "payTo": "0xYourAddress",
  "network": "solana",
  "asset": "USDC",
  "amount": "0",
  "amounts": {
    "weather.Weather.Forecast": "10000",
    "search.Search.Query": "5000"
  }
}

amount is the default (here "0" — free unless priced), and amounts sets per-tool overrides keyed by tool name. There is no “pricing” abstraction; it’s the x402 amount, resolved per tool, in the protocol’s own vocabulary. The standalone gateway accepts the same file via --x402-config or the X402_CONFIG environment variable.

Notes

See also