README.md

Using Tenderly to Trace Transactions

Optimism transactions sometimes fail. In this tutorial you learn how to use Tenderly to see what happened, what is the cause of the failure.

The contract we'll use as a sample for debugging is Fail.sol.

As samples, we have two transactions using this contract:

Get a Tenderly account if you don't have an account already. The free tier is sufficient for what we do in this tutorial.

Search for the transaction hash. If Tenderly has that transaction, it will find it and tell you on what network it happened. For the purpose of this tutorial, search for the failed transaction (0x9af716b7ef0ab4b4af9fbf95a7aa3f401140b07e055674c449299e18f918b938).

If the source code isn't in Tenderly, it can download it from Etherscan:
1. Click the Debugger on the left sidebar.
2. Click in the function trace on a contract where you don't have the source code yet.
3. Click Fetch the contract from public explorer. Note that sometimes it takes a few minutes to fetch the source code.
In the overview you can see the stack trace. The different icons stand for different contract addresses (all implementing the same Fail contract in this case).
Below that you can see the function trace, including where exactly in the source the failure was and what happened before that.

Because of the way we called cheapFail when it reverts it causes the entire transaction to revert. There is a way to call subcontracts without propagating revert, see here for directions.

Trace the successful transaction (0x86b4fc03c1656b64206cdedd1ef840563c1aa32a7ab7c2ca4c2dcb205752848d).
Select State Changes on the left bar to see the state changes caused by the transaction.
Select Debugger on the left bar to see the function trace (which functions ran, which functions called which, etc.), the stack trace (the current funtion and who called it), the source code, and the