# Overview

`mega-evme` can record detailed execution traces during EVM runs. Traces are useful for debugging reverts, analyzing gas consumption, and understanding call flow.

## Enabling Tracing

Add `--trace` to any command to enable tracing:

```bash
mega-evme run 0x60016000526001601ff3 --trace
```

By default, this uses the [opcode tracer](https://docs.megaeth.com/mega-evme/tracing/opcode-tracer). Use `--tracer` to pick a different tracer.

## Tracers

| Tracer                                                                  | `--tracer` value                | Description                                                            |
| ----------------------------------------------------------------------- | ------------------------------- | ---------------------------------------------------------------------- |
| [Opcode](https://docs.megaeth.com/mega-evme/tracing/opcode-tracer)      | `opcode` (default)              | Step-by-step opcode execution log with gas, stack, memory, and storage |
| [Call](https://docs.megaeth.com/mega-evme/tracing/call-tracer)          | `call`                          | Nested call tree showing CALL/CREATE hierarchy, gas, and return data   |
| [Pre-State](https://docs.megaeth.com/mega-evme/tracing/prestate-tracer) | `pre-state` (alias: `prestate`) | Account state accessed during execution, with optional diff mode       |

## Common Options

These flags apply to all tracers:

| Flag                    | Default  | Description                                         |
| ----------------------- | -------- | --------------------------------------------------- |
| `--trace`               | `false`  | Enable tracing                                      |
| `--trace.output <PATH>` | stdout   | Write trace output to a file instead of the console |
| `--tracer <TRACER>`     | `opcode` | Select which tracer to use                          |

## Output

Trace output is JSON. When `--trace.output` is not set, the trace is printed to stdout after the execution result. When `--trace.output` is set, the trace is written to the specified file and only the execution result appears on stdout.

```bash
# Trace to file
mega-evme run 0x60016000526001601ff3 \
  --trace --tracer opcode \
  --trace.output trace.json

# Trace to stdout (default)
mega-evme run 0x60016000526001601ff3 --trace
```