x402 2.3.0

x402 Payment Protocol SDK for Python

x402 Python SDK

Core implementation of the x402 payment protocol. Provides transport-agnostic client, server, and facilitator components with both async and sync variants.

Installation

Install the core package with your preferred framework/client:

# HTTP clients (pick one)
uv add x402[httpx]      # httpx client
uv add x402[requests]   # requests client

# Server frameworks (pick one)
uv add x402[fastapi]    # FastAPI middleware
uv add x402[flask]      # Flask middleware

# Blockchain mechanisms (pick one or both)
uv add x402[evm]        # EVM/Ethereum
uv add x402[svm]        # Solana

# Multiple extras
uv add x402[fastapi,httpx,evm]

# Everything
uv add x402[all]

Quick Start

Client (Async)

from x402 import x402Client
from x402.mechanisms.evm.exact import ExactEvmScheme

client = x402Client()
client.register("eip155:*", ExactEvmScheme(signer=my_signer))

# Create payment from 402 response
payload = await client.create_payment_payload(payment_required)

Client (Sync)

from x402 import x402ClientSync
from x402.mechanisms.evm.exact import ExactEvmScheme

client = x402ClientSync()
client.register("eip155:*", ExactEvmScheme(signer=my_signer))

payload = client.create_payment_payload(payment_required)

Server (Async)

from x402 import x402ResourceServer, ResourceConfig
from x402.http import HTTPFacilitatorClient
from x402.mechanisms.evm.exact import ExactEvmServerScheme

facilitator = HTTPFacilitatorClient(url="https://x402.org/facilitator")
server = x402ResourceServer(facilitator)
server.register("eip155:*", ExactEvmServerScheme())
server.initialize()

# Build requirements
config = ResourceConfig(
    scheme="exact",
    network="eip155:8453",
    pay_to="0x...",
    price="$0.01",
)
requirements = server.build_payment_requirements(config)

# Verify payment
result = await server.verify_payment(payload, requirements[0])

Server (Sync)

from x402 import x402ResourceServerSync, ResourceConfig
from x402.http import HTTPFacilitatorClientSync
from x402.mechanisms.evm.exact import ExactEvmServerScheme

facilitator = HTTPFacilitatorClientSync(url="https://x402.org/facilitator")
server = x402ResourceServerSync(facilitator)
server.register("eip155:*", ExactEvmServerScheme())
server.initialize()

result = server.verify_payment(payload, requirements[0])

Facilitator (Async)

from x402 import x402Facilitator
from x402.mechanisms.evm.exact import ExactEvmFacilitatorScheme

facilitator = x402Facilitator()
facilitator.register(
    ["eip155:8453", "eip155:84532"],
    ExactEvmFacilitatorScheme(wallet=wallet),
)

result = await facilitator.verify(payload, requirements)
if result.is_valid:
    settle_result = await facilitator.settle(payload, requirements)

Facilitator (Sync)

from x402 import x402FacilitatorSync
from x402.mechanisms.evm.exact import ExactEvmFacilitatorScheme

facilitator = x402FacilitatorSync()
facilitator.register(
    ["eip155:8453", "eip155:84532"],
    ExactEvmFacilitatorScheme(wallet=wallet),
)

result = facilitator.verify(payload, requirements)

Async vs Sync

Each component has both async and sync variants:

Async (default)	Sync
x402Client	x402ClientSync
x402ResourceServer	x402ResourceServerSync
x402Facilitator	x402FacilitatorSync
HTTPFacilitatorClient	HTTPFacilitatorClientSync

Async variants support both sync and async hooks (auto-detected). Sync variants only support sync hooks and raise TypeError if async hooks are registered.

Framework Pairing

Framework	HTTP Client	Server	Facilitator Client
FastAPI	httpx	x402ResourceServer	HTTPFacilitatorClient
Flask	requests	x402ResourceServerSync	HTTPFacilitatorClientSync

Mismatched variants raise TypeError at runtime.

Client Configuration

Use from_config() for declarative setup:

from x402 import x402Client, x402ClientConfig, SchemeRegistration

config = x402ClientConfig(
    schemes=[
        SchemeRegistration(network="eip155:*", client=ExactEvmScheme(signer)),
        SchemeRegistration(network="solana:*", client=ExactSvmScheme(signer)),
    ],
    policies=[prefer_network("eip155:8453")],
)
client = x402Client.from_config(config)

Policies

Filter or prioritize payment requirements:

from x402 import prefer_network, prefer_scheme, max_amount

client.register_policy(prefer_network("eip155:8453"))
client.register_policy(prefer_scheme("exact"))
client.register_policy(max_amount(1_000_000))  # 1 USDC max

Lifecycle Hooks

Client Hooks

from x402 import AbortResult, RecoveredPayloadResult

def before_payment(ctx):
    print(f"Creating payment for: {ctx.selected_requirements.network}")
    # Return AbortResult(reason="...") to cancel

def after_payment(ctx):
    print(f"Payment created: {ctx.payment_payload}")

def on_failure(ctx):
    print(f"Payment failed: {ctx.error}")
    # Return RecoveredPayloadResult(payload=...) to recover

client.on_before_payment_creation(before_payment)
client.on_after_payment_creation(after_payment)
client.on_payment_creation_failure(on_failure)

Server Hooks

server.on_before_verify(lambda ctx: print(f"Verifying: {ctx.payload}"))
server.on_after_verify(lambda ctx: print(f"Result: {ctx.result.is_valid}"))
server.on_verify_failure(lambda ctx: print(f"Failed: {ctx.error}"))

server.on_before_settle(lambda ctx: ...)
server.on_after_settle(lambda ctx: ...)
server.on_settle_failure(lambda ctx: ...)

Facilitator Hooks

facilitator.on_before_verify(...)
facilitator.on_after_verify(...)
facilitator.on_verify_failure(...)
facilitator.on_before_settle(...)
facilitator.on_after_settle(...)
facilitator.on_settle_failure(...)

Network Pattern Matching

Register handlers for network families using wildcards:

# All EVM networks
client.register("eip155:*", ExactEvmScheme(signer))

# Specific network (takes precedence)
client.register("eip155:8453", CustomScheme())

HTTP Headers

V2 Protocol (Current)

Header	Description
PAYMENT-SIGNATURE	Base64-encoded payment payload
PAYMENT-REQUIRED	Base64-encoded payment requirements
PAYMENT-RESPONSE	Base64-encoded settlement response

V1 Protocol (Legacy)

Header	Description
X-PAYMENT	Base64-encoded payment payload
X-PAYMENT-RESPONSE	Base64-encoded settlement response

Related Modules

• x402.http - HTTP clients, middleware, and facilitator client
• x402.mechanisms.evm - EVM/Ethereum implementation
• x402.mechanisms.svm - Solana implementation
• x402.extensions - Protocol extensions (Bazaar discovery)

Examples

See examples/python.