Source Debugger

View calls, source code, call stacks, and variables in one workspace.

# Source Debugger

View calls, source code, call stacks, and variables in one workspace.

Source Debugger helps you continue investigating a specific contract call. It does not replay the transaction; it puts the existing Trace, source, and variables together so you can confirm what happened at that step.

## Get to know the workspace

Debugger has a few key areas:

| Area            | What it is for                                          |
| --------------- | ------------------------------------------------------- |
| Execution Trace | Select a call and see where it sits in the transaction. |
| Sources         | Browse source files available for the transaction.      |
| Editors         | Open the source location for the selected call.         |
| Call Stack      | See which parent calls led to this call.                |
| Information     | Check call inputs, outputs, and contract variables.     |

Select a call in Execution Trace first. When source is available, Editors opens the matching file. Use Call Stack and Information to verify its context. If source is unavailable, switch to **Bytecode Mode** to inspect instructions, Stack, Memory, and Storage.

## Follow an example

The example below reuses the Debugger workspace with local Trace and source fixtures. Follow these steps:

<div className="not-prose my-6 grid gap-3 sm:grid-cols-2">
  <a href="#find-callback" className="border-border-secondary hover:border-fg-info-secondary hover:bg-bg-secondary-subtle flex rounded-xl border p-4 no-underline">
    <span className="text-fg-info-secondary mr-3 font-semibold">
      1
    </span>

    <span>
      <strong className="block text-sm">
        Find the callback
      </strong>

      <span className="text-text-secondary text-sm">
        Select the flash callback in Trace.
      </span>
    </span>
  </a>

  <a href="#read-source" className="border-border-secondary hover:border-fg-info-secondary hover:bg-bg-secondary-subtle flex rounded-xl border p-4 no-underline">
    <span className="text-fg-info-secondary mr-3 font-semibold">
      2
    </span>

    <span>
      <strong className="block text-sm">
        Read the source
      </strong>

      <span className="text-text-secondary text-sm">
        See what this call does in order.
      </span>
    </span>
  </a>

  <a href="#check-context" className="border-border-secondary hover:border-fg-info-secondary hover:bg-bg-secondary-subtle flex rounded-xl border p-4 no-underline">
    <span className="text-fg-info-secondary mr-3 font-semibold">
      3
    </span>

    <span>
      <strong className="block text-sm">
        Check the context
      </strong>

      <span className="text-text-secondary text-sm">
        Verify it with Call Stack and Information.
      </span>
    </span>
  </a>

  <a href="#continue-trace" className="border-border-secondary hover:border-fg-info-secondary hover:bg-bg-secondary-subtle flex rounded-xl border p-4 no-underline">
    <span className="text-fg-info-secondary mr-3 font-semibold">
      4
    </span>

    <span>
      <strong className="block text-sm">
        Continue tracing
      </strong>

      <span className="text-text-secondary text-sm">
        Follow the staking, swap, and unwrap calls.
      </span>
    </span>
  </a>
</div>

> Interactive content: Source Debugger walkthrough. Open the online documentation to view it.

<span id="find-callback" />

### Find the callback

Expand `UniswapV3Pool.flash(...)` and select `uniswapV3FlashCallback(...)`. Confirm that the Pool is the From address and the intermediate contract is the To address.

<span id="read-source" />

### Read the source

After selection, **Editors** opens `XPepeExploit.sol`. This step stakes and withdraws, swaps for WETH, then sends out ETH.

<span id="check-context" />

### Check the context

In **Call Stack**, confirm `flash` → `uniswapV3FlashCallback`. In **Information**, check the inputs for this call.

<span id="continue-trace" />

### Continue tracing

Continue with `TokenStaker.stake(...)`, `withdrawAll()`, `Pool.swap(...)`, and `WETH.withdraw(...)` to understand the order of staking, swapping, and unwrapping. Finally, use [State Changes](/docs/transaction/state-changes) to confirm the state that was actually written.

## Notes

* Source locations depend on verified source, compiler information, and Source Maps. When they are unavailable, Trace, parameters, and raw data remain useful.
* Call Stack shows nesting; use Execution Trace for the order of sibling calls.
* Source Debugger explains execution. Use Balance Changes or Token Flow for the final asset outcome.

## Next steps

* [Bytecode Debugger](/docs/transaction/bytecode-debugger)
* [State Changes](/docs/transaction/state-changes)

Source Debugger helps you continue investigating a specific contract call. It does not replay the transaction; it puts the existing Trace, source, and variables together so you can confirm what happened at that step.

Get to know the workspace

Debugger has a few key areas:

Area	What it is for
Execution Trace	Select a call and see where it sits in the transaction.
Sources	Browse source files available for the transaction.
Editors	Open the source location for the selected call.
Call Stack	See which parent calls led to this call.
Information	Check call inputs, outputs, and contract variables.

Select a call in Execution Trace first. When source is available, Editors opens the matching file. Use Call Stack and Information to verify its context. If source is unavailable, switch to Bytecode Mode to inspect instructions, Stack, Memory, and Storage.

Follow an example

The example below reuses the Debugger workspace with local Trace and source fixtures. Follow these steps:

1Find the callback

Select the flash callback in Trace.

2Read the source

See what this call does in order.

3Check the context

Verify it with Call Stack and Information.

4Continue tracing

Follow the staking, swap, and unwrap calls.

Find the callback

Expand UniswapV3Pool.flash(...) and select uniswapV3FlashCallback(...). Confirm that the Pool is the From address and the intermediate contract is the To address.

Read the source

After selection, Editors opens XPepeExploit.sol. This step stakes and withdraws, swaps for WETH, then sends out ETH.

Check the context

In Call Stack, confirm flash → uniswapV3FlashCallback. In Information, check the inputs for this call.

Continue tracing

Continue with TokenStaker.stake(...), withdrawAll(), Pool.swap(...), and WETH.withdraw(...) to understand the order of staking, swapping, and unwrapping. Finally, use State Changes to confirm the state that was actually written.

Notes

Source locations depend on verified source, compiler information, and Source Maps. When they are unavailable, Trace, parameters, and raw data remain useful.
Call Stack shows nesting; use Execution Trace for the order of sibling calls.
Source Debugger explains execution. Use Balance Changes or Token Flow for the final asset outcome.

Next steps

Call Graph

Quickly inspect the call relationships and main execution paths between addresses in a transaction.

Bytecode Debugger

Inspect calls, stack, memory, and storage instruction by instruction when source code is unavailable or you need to verify low-level execution.

On this page

Get to know the workspace

Follow an example

Find the callback

Read the source

Check the context

Continue tracing