langchain-paypack 0.5.0

LangChain tool for PayPack: AI Agent autonomous payments (HTTP 402, x402, AP2)

PayPack

Universal Payment Middleware for AI Agents

One line of code. Let your AI pay for itself.

---

The Problem

The HTTP 402 status code has existed in the protocol specification since 1991. For over three decades, it has never been used in practice.

Why? Because when a server returns "Payment Required," there must be a human on the other end of the screen to pull out a credit card.

AI Agents change everything.

An autonomous AI agent can make hundreds of API calls, data purchases, and content subscriptions per hour — with individual amounts as small as $0.001. Traditional payment systems collapse under micro-transaction fees and the need for manual approval.

x402 (proposed by Coinbase) and AP2 (proposed by Google) are solving this: the server returns 402 with a payee address and amount, and the AI agent completes the on-chain payment automatically — all within a single HTTP round trip. No human intervention required.

PayPack's mission: to be the thinnest, most reliable, most indispensable middleware layer in the AI payment stack.

---

Architecture

       AI Agent Application
                │
                ▼
         PayPack SDK  ◄── You are here
                │
        ┌───────┼───────┐
        │       │       │
  Protocol   Payment   Security
   Parser    Router    Fuse
  (x402/    (USDC/    (Limits/
   AP2)      Fiat)     Audit)
        │       │       │
        └───────┼───────┘
                │
                ▼
    Settlement Networks
  (Base / Solana / Alipay+)

PayPack doesn't invent new protocols. It wraps scattered capabilities into a single agent.pay().

---

Features

• Multi-Protocol: Supports both x402 and AP2 with automatic detection
• Signer Abstraction: Pluggable signing — LocalSigner for dev, AWSKMSSigner for production (private key never leaves HSM)
• Nano-Payment Optimized: Built for sub-$0.01 transactions with ERC-4337 batch settlement to save gas
• Security Fuse: Daily spend limits, balance checks, auditable receipts
• Full Audit Trail: Every payment generates a queryable JSON receipt
• LangChain Native: Drop-in PayPackTool for LangChain agents
• Dual Compliance Track: USDC on-chain + Alipay AI Pay (planned)

---

Installation

pip install https://gitee.com/rhcjw_com/paypack/raw/master/dist/langchain_paypack-0.5.0-py3-none-any.whl

Note: Includes the full paypack SDK (core + signer + nanopay).

---

Quick Start

from paypack import AgentPay

# Initialize
pay = AgentPay(
    wallet_config={"private_key": "your-key"},
    network="base-sepolia",
    spend_limit_daily=10.0,
    broadcast=False
)

# Scenario 1: Auto-handle HTTP 402
import requests
response = requests.get("https://api.data-provider.com/premium")
if response.status_code == 402:
    content = pay.auto_handle_402(response)

# Scenario 2: Direct nano-payment
receipt = pay.send(
    to="0xRecipientAddress",
    amount=0.001,
    currency="USDC"
)
print(receipt["tx_hash"])

LangChain Integration

from langchain_paypack import PayPackTool

tool = PayPackTool(
    private_key="0x...",
    wallet_address="0x...",
    network="base-sepolia",
    spend_limit_daily=10.0,
    broadcast=False
)

# AI agent calls this directly
result = tool._run(to="0x...", amount=0.001, currency="USDC")
print(result)

---

Supported Networks

Network	Chain ID	Currency
Base Sepolia (testnet)	84532	ETH, USDC
Base Mainnet	8453	ETH, USDC
Ethereum Mainnet	1	ETH, USDC
Polygon Mainnet	137	POL, USDC
Arbitrum Mainnet	42161	ETH, USDC

---

Milestones

✅ v0.1.0 (2026-06-20) — ETH + USDC offline signing verified on Base Sepolia testnet

✅ v0.2.0 — AP2 protocol parser completed

✅ v0.3.0 (2026-06-21) — LangChain tool plugin tested, multi-chain support, balance checks, environment variable key support

✅ v0.4.0 (2026-07-08) — Signer abstraction (LocalSigner + AWSKMSSigner), ERC-4337 batch settlement (Batcher + Bundler)

✅ v0.5.0 (2026-07-08) — RPC failover (multi-node auto-switch), transaction retry (RBF + exponential backoff), limit persistence (Redis/SQLite)

Currency	Amount	Offline-Signed TX Hash
ETH	0.0001 ETH	d5f7ec94342c26a132289a9898ffd4885010089d1ddba19951117618a3992127
USDC	0.001 USDC	c4c24c4c1c8fd2ae738ed91cd87596ad2c672337b5ebf6d42a392adf61760e27

📌 Production-ready: RPC failover, retry, persistent limits, KMS signing — all in place.

Roadmap

Phase	Goal	Status
v0.1	Base testnet x402 payment loop (ETH + USDC)	✅ Done
v0.2	AP2 protocol support	✅ Done
v0.3	LangChain plugin release	✅ Done
v0.4	Signer abstraction + ERC-4337 batch settlement	✅ Done
v0.5	RPC failover + retry + limit persistence	✅ Done
v0.6	Alipay AI Pay integration	🚧 Planned
v1.0	PayPack Cloud (hosted service)	🚧 Planned

---

Why Now?

• Stablecoin annual transaction volume surpassed $33 trillion (2025) — 20x PayPal
• AI agent count projected to reach 22 billion (McKinsey)
• x402 protocol already processes tens of millions of transactions on Solana
• LangChain/LlamaIndex payment plugin market is completely vacant

Infrastructure is ready. Demand is exploding. The payment layer lacks a standard answer.

---

Contributing

Star this repo, open an issue, or reach out if you're building in the agent economy.

License

Apache License 2.0. See LICENSE.