use-python-x402-core-avm

name

use-python-x402-core-avm

description

Use the x402-avm Python package core and AVM mechanism directly for custom integrations. Use when working with x402 core components (x402Client, x402ResourceServer, x402Facilitator), implementing AVM signer protocols, using constants (ALGORAND_TESTNET_CAIP2, USDC ASA IDs), calling utility functions (address validation, amount conversion, transaction encoding), building custom payment flows, creating transaction groups, or understanding fee abstraction. Strong triggers include "use x402 Python SDK directly", "x402 core components", "AVM signer protocol", "Algorand constants", "transaction encoding", "fee abstraction", "custom x402 integration", "ExactAvmScheme", "to_atomic_amount", "decode_transaction_bytes".

Using x402-avm Python Core and AVM Mechanism

Use the x402-avm Python package core components and AVM mechanism directly for building custom payment integrations on Algorand.

Prerequisites

Before using this skill, ensure:

1. Python 3.10+ is installed
2. x402-avm package is available: pip install "x402-avm[avm]"
3. Understanding of x402 payment flow -- client sends payment, server returns 402, facilitator verifies/settles

Core Architecture

The x402-avm Python SDK has two layers:

x402-avm Core                          AVM Mechanism
+----------------------------------+   +----------------------------------+
| x402Client / x402ClientSync      |   | ClientAvmSigner (Protocol)       |
| x402ResourceServer / ...Sync     |   | FacilitatorAvmSigner (Protocol)  |
| x402Facilitator / ...Sync        |   | ExactAvmScheme                   |
| schemas, types                   |   | constants, utils                 |
+----------------------------------+   +----------------------------------+
         |                                        |
         +--- register_exact_avm_* ---------------+

How to Proceed

Step 1: Install the Package

# Core + AVM mechanism
pip install "x402-avm[avm]"

# With a web framework
pip install "x402-avm[avm,fastapi]"
pip install "x402-avm[avm,flask]"

Step 2: Understand the Signer Protocols

The SDK defines signer protocols (structural typing -- no inheritance required) that separate protocol definitions from implementations.

ClientAvmSigner -- for clients making payments:

from x402.mechanisms.avm.signer import ClientAvmSigner

class ClientAvmSigner(Protocol):
    @property
    def address(self) -> str:
        """58-character Algorand address."""
        ...

    def sign_transactions(
        self,
        unsigned_txns: list[bytes],
        indexes_to_sign: list[int],
    ) -> list[bytes | None]:
        """Sign specified transactions in a group."""
        ...

FacilitatorAvmSigner -- for facilitators verifying/settling payments:

from x402.mechanisms.avm.signer import FacilitatorAvmSigner

class FacilitatorAvmSigner(Protocol):
    def get_addresses(self) -> list[str]: ...
    def sign_transaction(self, txn_bytes: bytes, fee_payer: str, network: str) -> bytes: ...
    def sign_group(self, group_bytes: list[bytes], fee_payer: str, indexes_to_sign: list[int], network: str) -> list[bytes]: ...
    def simulate_group(self, group_bytes: list[bytes], network: str) -> None: ...
    def send_group(self, group_bytes: list[bytes], network: str) -> str: ...
    def confirm_transaction(self, txid: str, network: str, rounds: int = 4) -> None: ...

Step 3: Use Constants

from x402.mechanisms.avm.constants import (
    ALGORAND_TESTNET_CAIP2,     # "algorand:SGO1GKSzyE7IEPItTxCByw9x8FmnrCDexi9/cOUJOiI="
    ALGORAND_MAINNET_CAIP2,     # "algorand:wGHE2Pwdvd7S12BL5FaOP20EGYesN73ktiC1qzkkit8="
    USDC_TESTNET_ASA_ID,        # 10458941
    USDC_MAINNET_ASA_ID,        # 31566704
    MIN_TXN_FEE,                # 1000
    MAX_GROUP_SIZE,             # 16
    NETWORK_CONFIGS,
)

Step 4: Use Utility Functions

from x402.mechanisms.avm.utils import (
    is_valid_address,
    to_atomic_amount,
    from_atomic_amount,
    decode_transaction_bytes,
    normalize_network,
    get_usdc_asa_id,
)

# Validate address
is_valid_address("AAAA...")  # True/False

# Convert amounts
to_atomic_amount(1.50)     # 1500000
from_atomic_amount(100000) # 0.1

# Decode transactions
info = decode_transaction_bytes(raw_txn_bytes)
print(info.type, info.sender, info.fee, info.is_signed)

Step 5: Register Schemes

from x402 import x402Client
from x402.mechanisms.avm.exact import register_exact_avm_client

client = x402Client()
register_exact_avm_client(client, signer)

# Now client.fetch() handles 402 responses automatically
response = await client.fetch("https://api.example.com/paid-resource")

Step 6: Understand Fee Abstraction

Fee abstraction uses Algorand's atomic transaction groups and pooled fees:

Transaction 0: USDC transfer (client -> resource owner, fee = 0)
Transaction 1: Self-payment (fee payer -> fee payer, fee covers both txns)

Client signs Txn 0, Facilitator signs Txn 1
Both execute atomically (all-or-nothing)

Important Rules / Guidelines

1. Signer separation -- Protocol definitions live in the SDK (signer.py), implementations live in examples. Zero algosdk imports in SDK core.
2. First-class AVM -- AVM is treated identically to EVM/SVM. Never conditional, always registered unconditionally.
3. algosdk encoding boundaries -- msgpack_decode() expects base64 string. msgpack_encode() returns base64 string. The SDK protocol passes raw msgpack bytes between methods. Convert at boundaries.
4. Import constants from SDK -- Use ALGORAND_TESTNET_CAIP2 from imports, not hardcoded strings, in SDK code.
5. Raw bytes contract -- The x402 SDK passes raw msgpack bytes between signer methods. This matches the @txnlab/use-wallet ecosystem standard.

Common Errors / Troubleshooting

Error	Cause	Solution
ImportError: x402.mechanisms.avm	Missing [avm] extra	Install with pip install "x402-avm[avm]"
msgpack_decode expects string	Passing raw bytes	Wrap: base64.b64encode(raw).decode()
Invalid address	Wrong address format	Must be 58-character Algorand address
to_atomic_amount overflow	Value too large	Check decimal places (6 for USDC/ALGO)
Network not supported	Unregistered network	Register with register_exact_avm_* first

References / Further Reading

• REFERENCE.md -- Detailed API reference for all exports
• EXAMPLES.md -- Complete code examples
• x402-avm AVM Documentation
• Examples Repository