create-python-x402-server

name

create-python-x402-server

description

Create x402 payment-protected servers with FastAPI (async) or Flask (sync) for Algorand. Use when building resource servers that require USDC payments, setting up payment middleware, configuring route pricing, or protecting API endpoints with x402. Strong triggers include "create a FastAPI server with x402 payments", "add payment middleware to Flask", "protect my API endpoint with Algorand USDC", "set up x402 resource server in Python", "PaymentMiddlewareASGI setup", "Flask PaymentMiddleware", "how do I accept Algorand payments on my API?", "multi-network payment server", "x402 route configuration".

Creating x402 Payment-Protected Servers in Python

Build FastAPI (async) or Flask (sync) servers that protect API endpoints behind Algorand USDC payments using x402 middleware.

Prerequisites

Before using this skill, ensure:

1. Python 3.10+ is installed
2. An Algorand address to receive payments (the payTo address)
3. A facilitator URL -- use https://x402.org/facilitator or run your own
4. Understanding of FastAPI or Flask basics

Core Workflow: Middleware-Based Payment Protection

The middleware intercepts requests to protected routes, checks for payment headers, verifies payments through the facilitator, and settles on success.

Client Request
      |
      v
x402 Middleware (checks route config)
      |
      +-- Not protected -> Pass through to handler
      |
      +-- Protected, no payment -> Return 402 with PaymentRequirements
      |
      +-- Protected, has payment -> Verify via Facilitator
            |
            +-- Invalid -> Return 402
            |
            +-- Valid -> Call handler, then settle payment

How to Proceed

Step 1: Install Dependencies

For FastAPI (async):

pip install "x402-avm[fastapi,avm]"

For Flask (sync):

pip install "x402-avm[flask,avm]"

Step 2: Choose Your Framework Pattern

FastAPI uses async components:

• x402ResourceServer (async)
• HTTPFacilitatorClient (async)
• PaymentMiddlewareASGI or payment_middleware

Flask uses sync components:

• x402ResourceServerSync (sync)
• HTTPFacilitatorClientSync (sync)
• PaymentMiddleware or payment_middleware

Step 3: Set Up the Resource Server

Create a facilitator client, resource server, and register the AVM scheme:

FastAPI:

from x402.server import x402ResourceServer
from x402.http import HTTPFacilitatorClient, FacilitatorConfig
from x402.mechanisms.avm.exact import ExactAvmServerScheme

facilitator = HTTPFacilitatorClient(FacilitatorConfig(url="https://x402.org/facilitator"))
server = x402ResourceServer(facilitator)
server.register("algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI=", ExactAvmServerScheme())

Flask:

from x402.server import x402ResourceServerSync
from x402.http import HTTPFacilitatorClientSync, FacilitatorConfig
from x402.mechanisms.avm.exact import ExactAvmServerScheme

facilitator = HTTPFacilitatorClientSync(FacilitatorConfig(url="https://x402.org/facilitator"))
server = x402ResourceServerSync(facilitator)
server.register("algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI=", ExactAvmServerScheme())

Step 4: Define Route Configurations

Routes map HTTP method + path patterns to payment requirements:

from x402.http import PaymentOption
from x402.http.types import RouteConfig

routes = {
    "GET /api/weather": RouteConfig(
        accepts=PaymentOption(
            scheme="exact",
            network="algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI=",
            pay_to="YOUR_ALGORAND_ADDRESS",
            price="$0.01",
        ),
    ),
}

Step 5: Apply Middleware

FastAPI -- Option A (ASGI class, recommended):

from x402.http.middleware.fastapi import PaymentMiddlewareASGI
app.add_middleware(PaymentMiddlewareASGI, routes=routes, server=server)

FastAPI -- Option B (function-based):

from x402.http.middleware.fastapi import payment_middleware
x402_mw = payment_middleware(routes=routes, server=server)

@app.middleware("http")
async def x402_middleware(request, call_next):
    return await x402_mw(request, call_next)

Flask:

from x402.http.middleware.flask import PaymentMiddleware
PaymentMiddleware(app, routes, server)

Step 6: Define Route Handlers

Routes listed in the configuration require payment. Unlisted routes pass through freely.

FastAPI:

@app.get("/api/weather")
async def get_weather():
    return {"temperature": 72, "unit": "F"}

Flask:

@app.route("/api/weather")
def get_weather():
    return {"temperature": 72, "unit": "F"}

Important Rules / Guidelines

1. Match async/sync variants -- FastAPI uses x402ResourceServer + HTTPFacilitatorClient, Flask uses x402ResourceServerSync + HTTPFacilitatorClientSync
2. Route format -- Keys must be "METHOD /path" (e.g., "GET /api/weather", "POST /api/generate/*")
3. Wildcard paths -- Use /* suffix to match all sub-paths (e.g., "GET /api/premium/*")
4. Unlisted routes pass through -- Only routes in the config require payment
5. Register scheme before middleware -- Call server.register(...) before adding middleware
6. Price format -- Use "$0.01" for auto-conversion or AssetAmount(amount="10000", asset="10458941") for explicit control
7. CAIP-2 network IDs -- Use full CAIP-2 identifiers like "algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI="

Pricing Options

Simple String Price

PaymentOption(
    scheme="exact",
    network="algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI=",
    pay_to="YOUR_ADDRESS",
    price="$0.01",  # Auto-converts to 10000 microUSDC
)

Explicit AssetAmount

from x402.schemas import AssetAmount

PaymentOption(
    scheme="exact",
    network="algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI=",
    pay_to="YOUR_ADDRESS",
    price=AssetAmount(
        amount="50000",       # 50000 microUSDC = $0.05
        asset="10458941",     # USDC ASA ID on testnet
        extra={"name": "USDC", "decimals": 6},
    ),
)

Multi-Network (AVM + EVM + SVM)

routes = {
    "GET /api/data/*": RouteConfig(
        accepts=[
            PaymentOption(scheme="exact", pay_to=AVM_ADDRESS, price="$0.01",
                         network="algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI="),
            PaymentOption(scheme="exact", pay_to=EVM_ADDRESS, price="$0.01",
                         network="eip155:84532"),
            PaymentOption(scheme="exact", pay_to=SVM_ADDRESS, price="$0.01",
                         network="solana:EtWTRABZaYq6iMfeYKouRu166VU2xqa1"),
        ],
    ),
}

Common Errors / Troubleshooting

Error	Cause	Solution
TypeError: async errors in Flask	Using async variants with Flask	Use x402ResourceServerSync and HTTPFacilitatorClientSync
402 returned to all requests	Middleware applied but facilitator unreachable	Check FACILITATOR_URL and network connectivity
Route not protected	Path pattern mismatch	Verify route key format matches: "GET /exact/path" or "GET /prefix/*"
Settlement fails	Facilitator cannot reach Algorand network	Check facilitator logs and algod endpoint
ImportError on middleware	Missing extras	pip install "x402-avm[fastapi,avm]" or "x402-avm[flask,avm]"

References / Further Reading

• REFERENCE.md - Detailed API reference for middleware
• EXAMPLES.md - Complete code examples for FastAPI and Flask
• x402-avm Examples Repository
• x402 Algorand Documentation