x402 Agent Monetizer

Monetize FastAPI AI agent endpoints with the x402 payment protocol — get paid in USDC per request, no signups, no API keys, no human in the loop.

Found this useful? ☕ Buy me a coffee · 💜 GitHub Sponsors · USDC tip: 0x7aEDE9Bb3A0c28132643ED8e416e4728f03FC18f (Base)

What this is

Drop-in FastAPI middleware that puts a USDC paywall in front of your agent endpoints. When a client hits a paid route without payment, the server returns HTTP 402 Payment Required with the price + recipient address. The client (human or AI) signs a USDC transfer over EIP-3009, retries the request, and gets the response.

Built for Python AI agents on Base. Uses x402 v2.10+ and the Coinbase-hosted facilitator (1,000 free tx/month).

Why

The agent economy needs micro-payments, not subscriptions. x402 lets agents transact in under a second for fractions of a cent. This repo is the FastAPI-flavored shortest path.

Install

pip install -e ".[fastapi]"

Requires Python 3.10+.

Quick start (server)

from fastapi import FastAPI
from x402_agent_monetizer import paywall

app = FastAPI()

# Paywalled endpoint — caller must pay \$0.05 USDC on Base before getting the response
@app.get("/summarize")
@paywall(price="0.05", network="base", recipient="0x7aEDE9Bb3A0c28132643ED8e416e4728f03FC18f")
def summarize(text: str):
    # your agent logic here
    return {"summary": f"<summary of {len(text)} chars>"}

Run:

uvicorn examples.fastapi_agent:app --reload

Quick start (client)

from x402_agent_monetizer import Client

client = Client(private_key="0x...", network="base")
resp = client.get("http://localhost:8000/summarize", params={"text": "hello"})
print(resp.json())  # auto-paid + retried

See examples/agent_client.py for a full agent loop.

Supported networks

Network	Status
Base mainnet	✅
Base Sepolia	✅ (testnet)
Polygon	✅
Arbitrum	✅
Solana	✅

Pricing dict accepts USDC, EURC, or any ERC-20 with EIP-3009 / Permit2.

Repo layout

src/x402_agent_monetizer/   # paywall decorator + Client wrapper
examples/                   # runnable end-to-end demos
tests/                      # pytest smoke tests

Roadmap

• FastAPI paywall decorator
• Sync + async client wrappers
• Flask + Starlette middleware
• Replay-attack protection
• Per-caller rate limits + receipts
• Coinbase AgentKit integration

License

MIT — see LICENSE.