---
title: "Custom Block"
description: "A Template reference of how the template is structured. This a useful information for building a custom block or editing templates in code."
url: https://docs.topol.io/email-editor/template-reference/blocks/custom.html
---

# Topol Custom Block

**A custom block is an `mj-raw` block flagged with `custom: true` and a `key`** that identifies which registered custom block it came from.

```ts
interface TopolRawBlock extends TopolBlock {
  tagName: "mj-raw";
  attributes: {
    containerWidth: number;
  };
  content: string;
  custom: true;
  key: string;
}
```