# Subcent402 (subcent402.com)
> The Autonomous M2M Micro-Payment Protocol & Model Context Protocol (MCP) Paywall Standard.

## Overview
Subcent402 enables AI agents to autonomously pay for paid tools, APIs, and computation feeds in sub-cent fractions ($0.001 - $0.01) via HTTP 402, L402 Macaroons, and Base USDC without human checkouts or API keys.

## Quick Installation
- Tool Server SDK: `npm install @subcent402/sdk`
- Agent Client SDK: `npm install @subcent402/client`

## Core Code Examples
### 1. Monetize an MCP Tool (3 Lines):
```typescript
import { withSubcent402 } from "@subcent402/sdk";

export const scrapeTool = withSubcent402({
  priceUsd: 0.002,
  toolName: "tokenmarkdown_extract",
  recipientWallet: "0xYourWalletOrLightningAddress",
  rootSecret: process.env.SUBCENT402_ROOT_SECRET!
}, async (params) => {
  return await extractCleanMarkdown(params.url);
});
```

### 2. Equip an Agent with BudgetGuard:
```typescript
import { wrapMcpClient } from "@subcent402/client";

const agentClient = wrapMcpClient(rawMcpClient, {
  budget: { maxDailySpendUsd: 5.00, maxPerCallUsd: 0.05 }
});
```

## Protocol Specifications
- MCP Custom Error Code: `-32042 Payment Required`
- REST Header: `Authorization: L402 <macaroon_base64>:<preimage_hex>`
- Gateway Settlement: Base USDC (x402), Lightning Network (L402), Mock Credit Vault.
- Offline Verification: HMAC-SHA256 Macaroon signature chain verified in <0.2ms.