P402 Protocol

AI payment router. Route across 300+ models, settle per request in USDC on Base or USDC.e on Tempo.

P402 sits between your AI application and every LLM provider. It handles intelligent multi-provider routing (cost / quality / speed / balanced), on-chain micropayment settlement via the x402 protocol and mppx on Base and Tempo, and spending guardrails for autonomous agents.

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Why P402

Problem	P402 Solution
Hardcoded to one AI provider	Route across 300+ models automatically
$0.30 payment fees kill micropayments	USDC on Base: fractions of a cent per settlement
No spending limits for AI agents	Session budgets + AP2 mandate governance
Fragmented provider APIs	One OpenAI-compatible endpoint
No visibility into AI costs	Real-time analytics + optimization suggestions

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Quick Start (VS Code / Cursor / Windsurf)

Install the extension — the MCP server is embedded, tools appear in Copilot agent mode immediately, no config files required:

ext install p402-protocol.p402

Then run P402: Configure API Key from the command palette.

→ VS Code Marketplace · Open VSX

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Quick Start (Claude Desktop / any MCP client)

{
  "mcpServers": {
    "p402": {
      "command": "npx",
      "args": ["-y", "@p402/mcp-server"],
      "env": { "P402_API_KEY": "p402_live_..." }
    }
  }
}

→ MCP docs · MCP Registry

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Quick Start (SDK)

npm install @p402/sdk

import P402Client from '@p402/sdk';

const p402 = new P402Client({ apiKey: process.env.P402_API_KEY });

// Drop-in OpenAI replacement — P402 picks the best provider
const response = await p402.chat({
  messages: [{ role: 'user', content: 'Explain x402 payments in one sentence.' }],
  p402: { mode: 'cost' }   // cost | quality | speed | balanced
});

console.log(response.choices[0].message.content);
// p402_metadata: { provider: 'deepseek', cost_usd: 0.00031, latency_ms: 412 }

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Quick Start (CLI)

# Authenticate once
npx p402 login

# Chat using the cheapest provider
npx p402 chat "What is x402?" --mode cost

# Check facilitator health
npx p402 health

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Routing Modes

Mode	Optimizes For	Typical Provider
cost	Lowest price	DeepSeek V3, Haiku 4.5, GPT-4o-mini
quality	Best output	Claude Opus 4.6, GPT-5, Gemini 3 Pro
speed	Lowest latency	Groq LPU, Flash models
balanced	Equal weight (default)	Sonnet 4.6, GPT-4o, Gemini Flash

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Session Budgets

Enforce hard spending caps for autonomous agents:

// Create a $10 session — agent cannot spend a cent more
const session = await p402.createSession({ budget_usd: 10 });

// All chat requests are deducted from the session
const response = await p402.chat({
  messages,
  p402: { session_id: session.id, mode: 'cost' }
});

// Check remaining budget
const { budget } = await p402.getSession(session.id);
console.log(`$${budget.remaining_usd} remaining`);

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x402 Payments

x402 is a machine-native payment protocol using HTTP 402. AI agents pay for resources using gasless EIP-3009 USDC transfers on Base L2.

Client → signs EIP-3009 authorization
       → POST /api/v1/facilitator/verify
       → POST /api/v1/facilitator/settle
Facilitator → executes transferWithAuthorization
            → pays gas (user pays zero gas)
            → returns { success, txHash, receipt }

Network: Base Mainnet (Chain ID: 8453) · Asset: USDC 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913

→ x402 payments guide

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A2A Protocol

P402 implements the Google A2A spec over JSON-RPC 2.0. Agents communicate through structured tasks, discover capabilities via /.well-known/agent.json, and settle payments via the x402 extension.

// Discover P402's capabilities
GET https://p402.io/.well-known/agent.json

// Submit a task
POST https://p402.io/api/a2a
{ "jsonrpc": "2.0", "method": "tasks/send", "params": { ... } }

→ A2A protocol guide

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Packages

Package	Description	Version
@p402/sdk	TypeScript SDK — P402Client, types, EIP-712 mandate helpers
@p402/cli	CLI tool — login, chat, sessions, mandates, analytics
@p402/mcp-server	stdio MCP server — 6 tools over Model Context Protocol
@p402/mpp-method	mppx payment methods — Base EIP-3009 and Tempo TIP-20 multi-rail settlement
p402 VS Code extension	Embedded MCP server for VS Code, Cursor, and Windsurf — zero config

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Examples

Example	What It Shows
01-quickstart	Login → chat → view spend in ~20 lines
02-openai-migration	Drop-in OpenAI SDK replacement
03-nextjs-session-budget	Budget-capped AI in a Next.js App Router project
04-a2a-agents	Two agents communicating with x402 payment gate

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Docs

Guide
Getting Started	Account, API key, first request
Authentication	API keys, env vars, security
Routing Guide	Modes, scoring, providers, models
x402 Payments	EIP-3009, wire format, settlement
Sessions	Session lifecycle + budget enforcement
A2A Protocol	JSON-RPC, mandates, Bazaar
CLI Reference	Full CLI command reference
OpenAPI Spec	Machine-readable API schema

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Community

• Dashboard: p402.io/dashboard
• Docs: p402.io/docs
• Issues: GitHub Issues
• Security: See SECURITY.md for responsible disclosure
• Contributing: See CONTRIBUTING.md

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License

MIT © P402 Protocol