AVM Debugger

The AVM VSCode debugger enables inspection of blockchain logic through Simulate Traces - JSON files containing detailed transaction execution data without on-chain deployment. The extension requires both trace files and source maps that link original code (TEAL or Puya) to compiled instructions. While the extension works independently, projects created with algokit templates include utilities that automatically generate these debugging artifacts. For full list of available capabilities of debugger extension refer to this documentation.

This tutorial demonstrates the workflow using a Python-based Algorand project. We will walk through identifying and fixing a bug in an Algorand smart contract using the Algorand Virtual Machine (AVM) Debugger. We’ll start with a simple, smart contract containing a deliberate bug, and by using the AVM Debugger, we’ll pinpoint and fix the issue. This guide will walk you through setting up, debugging, and fixing a smart contract using this extension.

Prerequisites

• Visual Studio Code (version 1.80.0 or higher)
• Node.js (version 18.x or higher)
• algokit-cli installed
• Algokit AVM VSCode Debugger extension installed
• Basic understanding of Algorand smart contracts using Python

Note

The extension is designed to debug both raw TEAL sourcemaps and sourcemaps generated via Puya compiler on the Algorand Virtual Machine. It provides a step-by-step debugging experience by utilizing transaction execution traces and compiled source maps of your smart contract.

Step 1: Setup the Debugging Environment

Install the Algokit AVM VSCode Debugger extension from the VSCode Marketplace by going to extensions in VSCode, then search for Algokit AVM Debugger and click install. You should see the output like the following:

Step 2: Set Up the Example Smart Contract

We aim to debug smart contract code in a project generated via algokit init. Refer to set up Algokit. Here’s the Algorand Python code for an tictactoe smart contract. The bug is in the move method, where games_played is updated by 2 for guest and 1 for host (which should be updated by 1 for both guest and host).

Remove hello_world folder Create a new tic tac toe smart contract starter via algokit generate smart-contract -a contract_name "TicTacToe" Replace the content of contract.py with the code below.

Python

# pyright: reportMissingModuleSource=false
from typing import Literal, Tuple, TypeAlias

from algopy import (
    ARC4Contract,
    BoxMap,
    Global,
    LocalState,
    OnCompleteAction,
    Txn,
    UInt64,
    arc4,
    gtxn,
    itxn,
    op,
    subroutine,
    urange,
)

Board: TypeAlias = arc4.StaticArray[arc4.Byte, Literal[9]]
HOST_MARK = 1
GUEST_MARK = 2


class GameState(arc4.Struct, kw_only=True):
    board: Board
    host: arc4.Address
    guest: arc4.Address
    is_over: arc4.Bool
    turns: arc4.UInt8


class TicTacToe(ARC4Contract):
    def __init__(self) -> None:
        self.id_counter = UInt64(0)

        self.games_played = LocalState(UInt64)
        self.games_won = LocalState(UInt64)

        self.games = BoxMap(UInt64, GameState)

    @subroutine
    def opt_in(self) -> None:
        self.games_played[Txn.sender] = UInt64(0)
        self.games_won[Txn.sender] = UInt64(0)

    @arc4.abimethod(allow_actions=[OnCompleteAction.NoOp, OnCompleteAction.OptIn])
    def new_game(self, mbr: gtxn.PaymentTransaction) -> UInt64:
        if Txn.on_completion == OnCompleteAction.OptIn:
            self.opt_in()

        self.id_counter += 1

        assert mbr.receiver == Global.current_application_address
        pre_new_game_box, exists = op.AcctParamsGet.acct_min_balance(
            Global.current_application_address
        )
        assert exists
        self.games[self.id_counter] = GameState(
            board=arc4.StaticArray[arc4.Byte, Literal[9]].from_bytes(op.bzero(9)),
            host=arc4.Address(Txn.sender),
            guest=arc4.Address(),
            is_over=arc4.Bool(False),  # noqa: FBT003
            turns=arc4.UInt8(),
        )
        post_new_game_box, exists = op.AcctParamsGet.acct_min_balance(
            Global.current_application_address
        )
        assert exists
        assert mbr.amount == (post_new_game_box - pre_new_game_box)

        return self.id_counter

    @arc4.abimethod
    def delete_game(self, game_id: UInt64) -> None:
        game = self.games[game_id].copy()

        assert game.guest == arc4.Address() or game.is_over.native
        assert Txn.sender == self.games[game_id].host.native

        pre_del_box, exists = op.AcctParamsGet.acct_min_balance(
            Global.current_application_address
        )
        assert exists
        del self.games[game_id]
        post_del_box, exists = op.AcctParamsGet.acct_min_balance(
            Global.current_application_address
        )
        assert exists

        itxn.Payment(
            receiver=game.host.native, amount=pre_del_box - post_del_box
        ).submit()

    @arc4.abimethod(allow_actions=[OnCompleteAction.NoOp, OnCompleteAction.OptIn])
    def join(self, game_id: UInt64) -> None:
        if Txn.on_completion == OnCompleteAction.OptIn:
            self.opt_in()

        assert self.games[game_id].host.native != Txn.sender
        assert self.games[game_id].guest == arc4.Address()

        self.games[game_id].guest = arc4.Address(Txn.sender)

    @arc4.abimethod
    def move(self, game_id: UInt64, x: UInt64, y: UInt64) -> None:
        game = self.games[game_id].copy()

        assert not game.is_over.native

        assert game.board[self.coord_to_matrix_index(x, y)] == arc4.Byte()

        assert Txn.sender == game.host.native or Txn.sender == game.guest.native
        is_host = Txn.sender == game.host.native

        if is_host:
            assert game.turns.native % 2 == 0
            self.games[game_id].board[self.coord_to_matrix_index(x, y)] = arc4.Byte(
                HOST_MARK
            )
        else:
            assert game.turns.native % 2 == 1
            self.games[game_id].board[self.coord_to_matrix_index(x, y)] = arc4.Byte(
                GUEST_MARK
            )

        self.games[game_id].turns = arc4.UInt8(
            self.games[game_id].turns.native + UInt64(1)
        )

        is_over, is_draw = self.is_game_over(self.games[game_id].board.copy())
        if is_over:
            self.games[game_id].is_over = arc4.Bool(True)
            self.games_played[game.host.native] += UInt64(1)
            self.games_played[game.guest.native] += UInt64(2) # incorrect code here

            if not is_draw:
                winner = game.host if is_host else game.guest
                self.games_won[winner.native] += UInt64(1)

    @arc4.baremethod(allow_actions=[OnCompleteAction.CloseOut])
    def close_out(self) -> None:
        pass

    @subroutine
    def coord_to_matrix_index(self, x: UInt64, y: UInt64) -> UInt64:
        return 3 * y + x

    @subroutine
    def is_game_over(self, board: Board) -> Tuple[bool, bool]:
        for i in urange(3):
            # Row check
            if board[3 * i] == board[3 * i + 1] == board[3 * i + 2] != arc4.Byte():
                return True, False

            # Column check
            if board[i] == board[i + 3] == board[i + 6] != arc4.Byte():
                return True, False

        # Diagonal check
        if board[0] == board[4] == board[8] != arc4.Byte():
            return True, False
        if board[2] == board[4] == board[6] != arc4.Byte():
            return True, False

        # Draw check
        if (
            board[0]
            == board[1]
            == board[2]
            == board[3]
            == board[4]
            == board[5]
            == board[6]
            == board[7]
            == board[8]
            != arc4.Byte()
        ):
            return True, True

        return False, False

Add the below deployment code in deploy.config file:

Python

import logging

import algokit_utils
from algosdk.v2client.algod import AlgodClient
from algosdk.v2client.indexer import IndexerClient
from algokit_utils import (
    EnsureBalanceParameters,
    TransactionParameters,
    ensure_funded,
)
from algokit_utils.beta.algorand_client import AlgorandClient
import base64

import algosdk.abi
from algokit_utils import (
    EnsureBalanceParameters,
    TransactionParameters,
    ensure_funded,
)
from algokit_utils.beta.algorand_client import AlgorandClient
from algokit_utils.beta.client_manager import AlgoSdkClients
from algokit_utils.beta.composer import PayParams
from algosdk.atomic_transaction_composer import TransactionWithSigner
from algosdk.util import algos_to_microalgos
from algosdk.v2client.algod import AlgodClient
from algosdk.v2client.indexer import IndexerClient

logger = logging.getLogger(__name__)

# define deployment behaviour based on supplied app spec
def deploy(
    algod_client: AlgodClient,
    indexer_client: IndexerClient,
    app_spec: algokit_utils.ApplicationSpecification,
    deployer: algokit_utils.Account,
) -> None:
    from smart_contracts.artifacts.tictactoe.tic_tac_toe_client import (
        TicTacToeClient,
    )

    app_client = TicTacToeClient(
        algod_client,
        creator=deployer,
        indexer_client=indexer_client,
    )

    app_client.deploy(
        on_schema_break=algokit_utils.OnSchemaBreak.AppendApp,
        on_update=algokit_utils.OnUpdate.AppendApp,
    )

    last_game_id = app_client.get_global_state().id_counter
    algorand = AlgorandClient.from_clients(AlgoSdkClients(algod_client, indexer_client))
    algorand.set_suggested_params_timeout(0)

    host = algorand.account.random()
    ensure_funded(
        algorand.client.algod,
        EnsureBalanceParameters(
            account_to_fund=host.address,
            min_spending_balance_micro_algos=algos_to_microalgos(200_000),
        ),
    )

    print(f"balance of host address: ",algod_client.account_info(host.address)["amount"]);
    print(f"host address: ",host.address);

    ensure_funded(
        algorand.client.algod,
        EnsureBalanceParameters(
            account_to_fund=app_client.app_address,
            min_spending_balance_micro_algos=algos_to_microalgos(10_000),
        ),
    )
    print(f"app_client address: ",app_client.app_address);

    game_id = app_client.opt_in_new_game(
        mbr=TransactionWithSigner(
            txn=algorand.transactions.payment(
                PayParams(
                    sender=host.address,
                    receiver=app_client.app_address,
                    amount=2_500 + 400 * (5 + 8 + 75),
                )
            ),
            signer=host.signer,
        ),
        transaction_parameters=TransactionParameters(
            signer=host.signer,
            sender=host.address,
            boxes=[(0, b"games" + (last_game_id + 1).to_bytes(8, "big"))],
        ),
    )

    guest = algorand.account.random()
    ensure_funded(
        algorand.client.algod,
        EnsureBalanceParameters(
            account_to_fund=guest.address,
            min_spending_balance_micro_algos=algos_to_microalgos(10),
        ),
    )

    app_client.opt_in_join(
        game_id=game_id.return_value,
        transaction_parameters=TransactionParameters(
            signer=guest.signer,
            sender=guest.address,
            boxes=[(0, b"games" + game_id.return_value.to_bytes(8, "big"))],
        ),
    )

    moves = [
        ((0, 0), (2, 2)),
        ((1, 1), (2, 1)),
        ((0, 2), (2, 0)),
    ]

    for host_move, guest_move in moves:
        app_client.move(
            game_id=game_id.return_value,
            x=host_move[0],
            y=host_move[1],
            transaction_parameters=TransactionParameters(
                signer=host.signer,
                sender=host.address,
                boxes=[(0, b"games" + game_id.return_value.to_bytes(8, "big"))],
                accounts=[guest.address],
            ),
        )

        # app_client.join(game_id=game_id.return_value)

        app_client.move(
            game_id=game_id.return_value,
            x=guest_move[0],
            y=guest_move[1],
            transaction_parameters=TransactionParameters(
                signer=guest.signer,
                sender=guest.address,
                boxes=[(0, b"games" + game_id.return_value.to_bytes(8, "big"))],
                accounts=[host.address],
            ),
        )

    game_state = algosdk.abi.TupleType(
        [
            algosdk.abi.ArrayStaticType(algosdk.abi.ByteType(), 9),
            algosdk.abi.AddressType(),
            algosdk.abi.AddressType(),
            algosdk.abi.BoolType(),
            algosdk.abi.UintType(8),
        ]
    ).decode(
        base64.b64decode(
            algorand.client.algod.application_box_by_name(
                app_client.app_id, box_name=b"games" + game_id.return_value.to_bytes(8, "big")
            )["value"]
        )
    )
    assert game_state[3]

Step 3: Compile & Deploy the Smart Contract

To enable debugging mode and full tracing for each step in the execution, go to main.py file and add:

from algokit_utils.config import config
config.configure(debug=True, trace_all=True)

For more details, refer to Debugger:

Next compile the smart contract using AlgoKit:

algokit project run build

This will generate the following files in artifacts: approval.teal, clear.teal, clear.puya.map, approval.puya.map and arc32.json files. The .puya.map files are result of the execution of puyapy compiler (which project run build command orchestrated and invokes automatically). The compiler has an option called --output-source-maps which is enabled by default.

Deploy the smart contract on localnet:

algokit project deploy localnet

This will automatically generate *.appln.trace.avm.json files in debug_traces folder, .teal and .teal.map files in sources.

The .teal.map files are source maps for TEAL and those are automatically generated every time an app is deployed via algokit-utils. Even if the developer is only interested in debugging puya source maps, the teal source maps would also always be available as a backup in case there is a need to fall back to more lower level source map.

Expected Behavior

The expected behavior is that games_played should be updated by 1 for both guest and host

Bug

When move method is called, games_played will get updated incorrectly for guest player.

Step 4: Start the debugger

In the VSCode, go to run and debug on left side. This will load the compiled smart contract into the debugger. In the run and debug, select debug TEAL via Algokit AVM Debugger. It will ask to select the appropriate debug_traces file.

Note

This vscode launch config is pre bundled with the template. And there is also an alternative execution option where a developer needs to open the json file representing the trace they want to debug and click on the debug button on the top right corner (which will appear specifically on trace json files when extension is installed).

Figure: Load Debugger in VSCode

Next it will ask you to select the source map file. Select the approval.puya.map file. Which would indicate to the debug extension that you would like to debug the given trace file using Puya sourcemaps, allowing you to step through high level python code. If you need to change the debugger to use TEAL or puya sourcemaps for other frontends such as Typescript, remove the individual record from .algokit/sources/sources.avm.json file or run the debugger commands via VSCode command palette

Step 5: Debugging the smart contract

Let’s now debug the issue:

Enter into the app_id of the transaction_group.json file. This opens the contract. Set a breakpoint in the move method. You can also add additional breakpoints.

On left side, you can see Program State which includes program counter, opcode, stack, scratch space. In On-chain State you will be able to see global, local and box storages for the application id deployed on localnet.

:::note: We have used localnet but the contracts can be deployed on any other network. A trace file is in a sense agnostic of the network in which the trace file was generated in. As long as its a complete simulate trace that contains state, stack and scratch states in the execution trace - debugger will work just fine with those as well. :::

Once you start step operations of debugging, it will get populated according to the contract. Now you can step-into the code.

Step 6: Analyze the Output

Observe the games_played variable for guest is increased by 2 (incorrectly) whereas for host is increased correctly.

Step 7: Fix the Bug

Now that we’ve identified the bug, let’s fix it in our original smart contract in move method:

Python

@arc4.abimethod
    def move(self, game_id: UInt64, x: UInt64, y: UInt64) -> None:
        game = self.games[game_id].copy()

        assert not game.is_over.native

        assert game.board[self.coord_to_matrix_index(x, y)] == arc4.Byte()

        assert Txn.sender == game.host.native or Txn.sender == game.guest.native
        is_host = Txn.sender == game.host.native

        if is_host:
            assert game.turns.native % 2 == 0
            self.games[game_id].board[self.coord_to_matrix_index(x, y)] = arc4.Byte(
                HOST_MARK
            )
        else:
            assert game.turns.native % 2 == 1
            self.games[game_id].board[self.coord_to_matrix_index(x, y)] = arc4.Byte(
                GUEST_MARK
            )

        self.games[game_id].turns = arc4.UInt8(
            self.games[game_id].turns.native + UInt64(1)
        )

        is_over, is_draw = self.is_game_over(self.games[game_id].board.copy())
        if is_over:
            self.games[game_id].is_over = arc4.Bool(True)
            self.games_played[game.host.native] += UInt64(1)
            self.games_played[game.guest.native] += UInt64(1) # changed here

            if not is_draw:
                winner = game.host if is_host else game.guest
                self.games_won[winner.native] += UInt64(1)

Step 8: Re-deploy

Re-compile and re-deploy the contract using the step 3.

Step 9: Verify again using Debugger

Reset the sources.avm.json file, then restart the debugger selecting approval.puya.source.map file. Run through steps 4 to 6 to verify that the games_played now updates as expected, confirming the bug has been fixed as seen below.

Note

You can alternatively also use approval.teal.map file instead of puya source map - for a lower-level TEAL debugging session. Refer to Algokit AVM VSCode Debugger commands via the VSCode command palette to automate clearing or editing the registry file.

Summary

In this tutorial, we walked through the process of using the AVM debugger from AlgoKit Python utils to debug an Algorand Smart Contract. We set up a debugging environment, loaded a smart contract with a planted bug, stepped through the execution, and identified the issue. This process can be invaluable when developing and testing smart contracts on the Algorand blockchain. It’s highly recommended to thoroughly test your smart contracts to ensure they function as expected and prevent costly errors in production before deploying them to the main network.

Next steps

To learn more, refer to documentation of the debugger extension to learn more about Debugging session.