Introduction

What is MCPay?

MCPay is a payment layer for MCP servers. It uses the long‑dormant HTTP 402 Payment Required status and the x402 pattern so that a client (human app or AI agent) can:

1. call a protected endpoint → 2) receive 402 + price metadata → 3) pay on‑chain (e.g. USDC) → 4) retry automatically → 5) get the result.

No subscriptions. No manual API keys. Works with autonomous agents.

Why MCPay (in 30 seconds)

• Developers: Ship paid tools in minutes. No OAuth, no recurring billing infra, no key juggling.
• MCP Hosts: Price each tool (per call / per token / dynamic) and get instant revenue.
• AI Agents: Do true agent↔service micropayments without human sign‑ups.

Use cases: paid search, embeddings, scraping, premium APIs, inference, downloads, rate‑limited features, one‑off unlocks.

How it works

                            ┌──────────────┐
                            │    Client    │
                            │ (app/agent)  │
                            └──────┬───────┘
                                   │
                                   ① unauthenticated HTTP request
                                   │
                                   ▼
        ┌─────────────────────────────────────────────┐
        │              MCP Proxy (Edge)               │
        │  • replies 402 + price metadata             │
        │  • signs & broadcasts payment               │
        │  • retries request once payment confirmed   │
        └──────┬──────────────┬───────────────────────┘
               │              │
               ② on-chain    ③ original request
               │   payment    │   (after pay)
               ▼              ▼
        ┌───────────────┐  ┌──────────────┐
        │  Blockchain   │  │   Your API   │
        │ (USDC/EUROe)  │  │ (any stack)  │
        └──────┬────────┘  └──────────────┘
               │
               │④ streamed usage & revenue events
               ▼
           (dashboard / analytics)

Under the hood we:

• Return 402 with structured price metadata (asset, amount, destination, memo, expiry).
• Accept the in‑flight payment, verify on‑chain, and retry the original request.
• Emit usage/revenue events for your dashboard.

Key components

1) Registry

Discover MCP servers and their priced tools at mcpay.tech/servers. Searchable, machine‑readable, agent‑friendly.

2) Builder (MCPay Build)

Create and iterate on new MCP servers quickly at mcpay.tech/build. Preview in a sandbox, publish, and (optionally) set prices per tool.

With MCPay Build you can:

• Create & iterate on MCP servers entirely in a chat flow.
• Preview them live in an isolated Vercel Sandbox.
• Deploy to GitHub + Vercel with one click.
• Monetize your tools instantly with MCPay (x402 per-call payments).

This lowers the barrier for developers who find MCP confusing or want to get started without boilerplate. The default template is a production-ready MCP server with free + paid tools side by side.

The MCP code lives in https://github.com/microchipgnu/mcpay-build

3) Monetizer (Proxy)

Wrap existing HTTP endpoints or MCP servers with the MCPay proxy to enforce pay‑per‑call. Zero code changes to your upstream service.

You can monetize via MCPay Registry or programmatically.