> For the complete documentation index, see [llms.txt](https://help.modelreef.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.modelreef.io/syntax/formula-syntax/formula-output-preview.md).

# Formula Output Preview

This article explains **formula output preview** in the Model Reef Formula editor.

You will learn:

* What the preview shows.
* How to use it to validate your formulas.
* How it fits into the wider modelling workflow.

The preview gives a quick visual check before you commit formula changes.

***

## What the preview displays

The formula preview usually shows:

* A basic chart or small table of the resulting time series.
* Key metadata about the series, such as its type or approximate range.
* Any warnings related to extreme values or unusual patterns.

It is not a full report, but a focused view to help verify correctness.

***

## When the preview updates

The preview updates when:

* The expression is syntactically valid.
* All references resolve to known variables or drivers.

As you edit the formula:

* The preview updates automatically after each valid change.
* If the formula becomes invalid, the preview may disappear until you fix the error.

This encourages an iterative edit-and-check workflow.

***

## Using the preview to validate logic

You can use the preview to check:

* Whether the general shape of the series matches expectations (for example growth, seasonality or step changes).
* Whether the magnitude of values appears sensible.
* Whether there are unexpected spikes or drops.

If the preview does not match your mental model of the series, revisit the formula or the drivers it uses.

***

## Limitations of the preview

The preview is not intended to:

* Replace full inspection of P\&L, Balance Sheet and Cashflow.
* Show every detail of the series across long horizons.
* Provide multi-scenario comparisons.

After saving a formula, you should still confirm its impact in core financial statements and key dashboards.

***

## Workflow with previews

{% stepper %}
{% step %}

### Open the Formula editor

Open the Formula editor for a variable.
{% endstep %}

{% step %}

### Compose or adjust the formula

Compose or modify the expression you want to use.
{% endstep %}

{% step %}

### Watch the preview

Watch the preview to ensure the resulting series looks right.
{% endstep %}

{% step %}

### Save the formula

Save the formula when you are happy with it.
{% endstep %}

{% step %}

### Confirm broader impact

Check financial statements and dashboards in the scenario to confirm the broader impact.
{% endstep %}
{% endstepper %}

Using the preview as an early check helps catch issues before they ripple through the model.

***

## Related articles

* [Understanding the Interface](/syntax/understanding-the-interface.md)
* [Units & Display](/syntax/variables-syntax/units-and-display.md)
* [COGS Mapping](/help/financial-outputs-and-valuation/cogs-mapping.md)
* [Build an Equity Valuation Model (FCFE)](/how-tos/valuation/build-an-equity-valuation-model-fcfe.md)