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Hello Starknet community, this repository is not updated with the latest Cairo syntax as well as informaiton about the updated relevant tools and hence, we do not recommend to attempt this tutorial as of today. If you are interested in contributing to the repository to update the tutorial, please create a PR and tag me @gyan0890 on it and we will be happy to support you with the process.

A great resource to get you up to speed with the new Cairo syntax in a Starknet context is Chapter 2 of the Starknet Book.

You can also ping me(@gyanlakshmi) on Telegram to help you assign the right tasks.

Starknet debugging

Welcome! This tutorial will show you how to use StarkNet development tools to debug a smart contract using 3 different testing frameworks:

We'll use a functionality of the Cairo language called hints, which allows you to inject python arbitrarily in your code. Hint usage is heavily restricted on StarkNet and is unapplicable in Smart Contracts. But it is extremely useful for debugging your contract. These debugging patterns are proposals we made, feel free to use any others you can think of and create a PR so everyone can know!


How it works

For each framework, there is a folder with broken or incomplete smart contracts that you need to fix. Each framework also includes a set of tests that the contract needs to pass.

Your objective is to use the debugging features outlined in the readme to understand the bug, fix it, and have the tests pass.

Where am I?

This workshop is the fifth in a series aimed at teaching how to build on StarkNet. Checkout out the following:

Topic GitHub repo
Learn how to read Cairo code Cairo 101
Deploy and customize an ERC721 NFT StarkNet ERC721
Deploy and customize an ERC20 token StarkNet ERC20
Build a cross layer application StarkNet messaging bridge
Debug your Cairo contracts easily (you are here) StarkNet debug
Design your own account contract StarkNet account abstraction

Providing feedback & getting help

Once you are done working on this tutorial, your feedback would be greatly appreciated!

Please fill out this form to let us know what we can do to make it better.

​ And if you struggle to move forward, do let us know! This workshop is meant to be as accessible as possible; we want to know if it's not the case.

​ Do you have a question? Join our Discord server, register, and join channel #tutorials-support ​ Are you interested in following online workshops about learning how to dev on StarkNet? Subscribe here


This project can be made better and will evolve as StarkNet matures. Your contributions are welcome! Here are things that you can do to help:

  • Create a branch with a translation to your language
  • Correct bugs if you find some
  • Add an explanation in the comments of the exercise if you feel it needs more explanation

​ ​

Getting started

Smart contracts that need fixing

The first smart contract array_contract.cairo is a dummy smart contract which has a view function that needs to:

  • Compute the product of each array element.
  • Add the current contract’s address to it.

The second smart contract mock_contract.cairo is also a dummy smart contract that will save a given array on initialization into a mapping and has a view function that needs:

  • Compute the product of each mapping element.

For each of those contracts and each framework, your goal is for the tests to pass successfully. ​ ​

Debugging with Hardhat


Run the following command in the hardhat directory to install all dependencies, as well cairo-lang and the starknet-devnet.

npm i
pip install "starknet-devnet>=0.2.1" cairo-lang

To setup a full cairo env you can take a look at this article.

Including hints in your contract

By default, StarkNet contracts can not use any hints in their code. cairo-lang refuses to compile contracts including hints.

However, starknet-devnet lets you run hints if you compile your contracts so that they include them.

Luckily, an flag has been added in hardhat to compile a contract that includes hints: --disable-hint-validation.

To debug a smart contract using hardhat you may want to print variables, there is an example in the smart contract.

Running tests

The following command will run the hardhat tests that need to pass, and execute any hints included in the contract in the terminal

npm run test

Your goal is to have this test pass.

The contracts to fix are here.

You can find the test file here.

​ ​



To run the python unit test files you'll need pytest and asynctest rich

pip install pytest asynctest cairo-lang

Running tests

The Python testing framework doesn't need to interact with the starknet-devnet as it can natively use the testing functions from the cairo-lang package so you can also use any python hint you want.

You can even add a breakpoint in a contract. How powerful is that? But wait that's not it you can also inspect the memory stack and the state variables! How cool is that?

You can run your python unit tests with pytest and inspect whatever you want in your contract.

The contracts to fix are here.

You can find the test script here.

Run the tests separately using:

pytest tests/ -s -W ignore::DeprecationWarning
pytest tests/ -s -W ignore::DeprecationWarning

Or all at once with:

pytest -s -W ignore::DeprecationWarning



To run the Protostar unit test files you'll need to install protostar, flask and requests:

pip install flask requests
curl -L | bash

Check the documentation for more details.

Running tests

As with the Python testing framework, Protostar doesn't need to interact with the starknet-devnet as it can natively use the testing functions from the cairo-lang package. When running the protostar test command, specify that you want to use unwhitelisted hints with the flag --disable-hint-validation (example below). Protostar doesn't give you full control over what's happening so you can't really use all the python code you wish. Nothing to worry about we've got for you a biiiiig 🧠 solution.

Adding a breakpoint and printing stuff is too mainstream right?

Here is a simple script that listens to your port 5000 and prints the body of all the post requests it gets.

The contracts to fix are here.

The tests scripts are here.

First, run the python server with (you could left it open in another terminal):

python3 bigBrainDebug/

Remember that your goal is for the tests to pass successfully. Run the tests separately using:

protostar test tests/test_array_contract.cairo --disable-hint-validation
protostar test tests/test_mock_contract.cairo --disable-hint-validation

Or all at once with:

protostar test --disable-hint-validation

If you are on MacOS and encountered [__NSCFConstantString initialize] may have been in progress in another thread when fork() was called. add OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES before protostar line, e.g.:

OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES protostar test --disable-hint-validation



The ape tutorial is not maintained. If you want it updated please open an issue

To run the ape unit test files you'll need ape installed and configured. This is how you can do it:

pip install eth-ape
ape plugins install cairo starknet

If you were starting from scratch you would have to init your project and update the ape-config.yaml file. Here it's already been done for your convenience.

If you want to learn a little bit more about ape here is a video that you can watch which explains the basis of ape for StarkNet.

Since ape hides everything printed by the devnet we can use print to debug the contract. I chose to save the logs in a file but we could also setup a server that would receive data from the smart-contract execution or whatever other technique you can think of.

Running tests

To run the tests run the following command:

ape test

The contracts to fix are here.

You can find the test script here.


Learn how to debug a StarkNet smart contract






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