> ## Documentation Index
> Fetch the complete documentation index at: https://bagel.softnanolab.com/llms.txt
> Use this file to discover all available pages before exploring further.

# DefaultLogger

> Default file-based logger for scalar and sequence data.

This logger writes:

* energies.csv with step, per-state energy terms, per-state total energies, and system\_energy
* per-state FASTA files with sequences
* per-state mask FASTA files with mutability masks

It does not write structures; use FoldingLogger for structure outputs.

## Parameters

<ResponseField name="log_interval" type="int" required>
  Interval (in steps) at which to log the current system.
</ResponseField>

## Methods

### on\_optimization\_start

**Parameters**

<ResponseField name="context" type="CallbackContext" required />

### on\_step\_end

**Parameters**

<ResponseField name="context" type="CallbackContext" required />

## Example

```python theme={null}
import bagel as bg

callbacks = [
    bg.callbacks.DefaultLogger(log_interval=10),
]
```