# Custom Charts

> Create custom, reusable chart templates with Holistics' Custom Charts feature using Vega or Vega-lite and Holistics syntax.

:::info Note
- Custom Chart feature is available to all customers in **Standard Plan and above**
- For customers who are eligible for this feature but cannot find it in-app, or customers in **Entry Plan** and would like to give this feature a spin, please let us know via this form: Holistics's Support Ticket
:::

## Introduction

While Holistics's default chart types are often good enough for quick data visualization and analysis, they may not cover many advanced use cases. This is where **Custom Chart** comes in to help you create **complex but reusable chart templates** that cater to your specific needs.

Custom Charts is powered by [**Vega**](https://vega.github.io/vega/) or [**Vega-lite**](https://vega.github.io/vega-lite/) specifications, with Holistics's specifications on top to allow end-users to configure and interact with the charts in the same way as Holistics's built-in charts.

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## Getting started

### Step 1: Define a custom chart

In **Development > Library > Custom Charts**, create a new `.chart.aml` file and define your chart using the `CustomChartDef` block. This definition is a reusable template and does not contain data by itself.

```aml
CustomChartDef my_bar_chart {
  label: 'My Bar Chart'
  description: '...' // optional

  fields { ... }
  options { ... }

  template: @vgl { ... };;  // use @vg instead for Vega syntax
}
```

To learn how to write a custom chart definition:

- [Understand Custom Chart](understand-custom-chart)
- [AML Custom Chart Reference](/reference/aml/custom-chart)
- [Video Tutorial: Create a Custom Chart](/guides/create-custom-chart-video)
- [Custom Chart Library](custom-charts/library)

### Step 2: Build a visualization from the definition

Once defined, the chart definition is available in the chart picker alongside built-in charts. When you add a custom chart to a visualization block, the generated code looks like this:

```aml
block my_block: VizBlock {
  viz: CustomChart {
    custom_chart: my_bar_chart  // reference the custom chart name
    dataset: my_dataset
    field x_axis: dimension_field
    field y_axis: measure_field
  }
}
```

## Supported Holistics features

Custom charts support the following Holistics features:

- Interactive features (Explore, Date-drill, Cross-filter, Drill-through, etc.)
- Data Alert and Data schedules for reports
- Export reports to PNG/PDF/Excel/CSV

## Syntax reference

For a full parameter reference for `CustomChartDef` and `CustomChart`, see the [AML Custom Chart Reference](/reference/aml/custom-chart).

:::tip
Hover over `CustomChartDef` or `CustomChart` in the code editor to see suggestions for available parameters.
:::