UI extensibility

As every user has different needs, the Front Matter extension allows you to extend the UI with your own custom elements and components which can be used in the Front Matter dashboards and the panel.

The approach we choose, is to let you register a JavaScript file which will be loaded in the dashboard and panel.

Extensibility points

Front Matter CMS allows you to extend the UI in the following places:

  • Content dashboard

    • Image
    • Footer
    • Draft status
    • Date
    • Title
    • Description
    • Tags
  • Panel

    • Custom panel view
    • Custom fields

Registering a custom UI extension

To start, you will need to create a JavaScript. To make it easier, you need to make use of the @frontmatter/extensibility dependency which makes all the necessary functions available.

Using the @frontmatter/extensibility dependency
import {
} from "https://cdn.jsdelivr.net/npm/@frontmatter/extensibility/+esm";

Once you have created the JavaScript file, you can register your UI script in the frontMatter.extensibility.scripts setting as follows:

Registering a custom UI extension
  "frontMatter.extensibility.scripts": [

The extensibility framework options

Development mode

To enable development mode, you can use the enableDevelopmentMode function. This will allow you to reload the webview and open the developer tools without the need to reload Visual Studio Code.

Enabling development mode

Once the development mode is enabled, you will see the developer bar at the top of the webview.

Developer mode enabled

Registering a card image

To register a custom card image, you can use the registerCardImage function. This functionality allows you to register your own image/element on the content card.

Registering a card image
registerCardImage(async (filePath, metadata) => {
  return `<span>Your HTML for the card image</span>`;
  • The filePath parameter contains the path to the file which is being rendered in the card.
  • The metadata parameter contains the metadata (front matter) of the file which is being rendered in the card.
    • On this metadata object, you can find the fmPreviewImage property which contains the webview URL of the current project. You can use this property to render your own image located in the project.

Example of a custom image rendering:

Custom card image

Example of using the fmPreviewImage property:

Using the fmPreviewImage property
import { registerCardImage, enableDevelopmentMode } from "https://cdn.jsdelivr.net/npm/@frontmatter/extensibility/+esm";

 * @param {string} filePath - The path of the file
 * @param {object} data - The metadata of the file
 * @returns {string} - The HTML to be rendered in the card footer
registerCardImage(async (filePath, metadata) => {
    const image = metadata.fmPreviewImage ? metadata.fmPreviewImage : `${metadata.fmWebviewUrl}/relPath/to/fallback.jpg`;
    return `<img src="${image}" alt="${metadata.title}" style="object-fit: cover;" class="h-36" />`;

Registering a card footer

To register a custom card footer, you can use the registerCardFooter function. This functionality allows you to register your own footer/element which will be rendered at the bottom of the content.

Registering a card footer
registerCardFooter(async (filePath, metadata) => {
  return `<span>Your HTML for the card footer</span>`;

Example of a custom footer rendering:

Custom card footer

Registering a panel view

To register a custom panel view, you can use the registerPanelView function. This functionality allows you to register your own panel view which will be rendered in the panel.

Registering a panel view
registerPanelView(async (metadata) => {
  return {
    title: "Custom View",
    content: `
        <h1>Custom view...</h1>
        <p>Here you can add your own custom view.</p>

Example of a custom panel view rendering:

Custom panel view

Registering a custom field

To register a custom field, you can use the registerCustomField function. This functionality allows you to register your own custom field which can be used when editing the front matter.

The custom field requires a bit more work, as it comes with a change handler for the field value updates. To make it easier, it is recommended to use for instance a library like lit to create your custom field.

Registering a custom field
import { registerCustomField } from "https://cdn.jsdelivr.net/npm/@frontmatter/extensibility/+esm";
import { css, html, LitElement } from "https://esm.run/lit";

let CustomFieldValueChange;

class CustomField extends LitElement {
  static styles = css`
    input {
      border: 1px solid transparent;
      box-sizing: border-box;
      font-family: var(--vscode-font-family);
      padding: var(--input-padding-vertical) var(--input-padding-horizontal);
      color: var(--vscode-input-foreground);
      outline: none;
      background-color: var(--vscode-input-background);
      width: 100%;

    input:focus {
      border: 1px solid var(--vscode-inputValidation-infoBorder);

  static properties = {
    inputValue: {
      type: String,

  constructor() {
    this.inputValue = "";

  _internalChange(e) {
    this.inputValue = e.target.value;

  render() {
    return html`
        @change=${(e) => this._internalChange(e)}
customElements.define("custom-field", CustomField);

 * @param {string} name - The name of the custom field to use in the content-type
 * @param {function} callback - The callback that will be used for rendering the
 * custom field
registerCustomField("customTextField", async (value, onChange) => {
  // Bind the event handler for the onChange evet
  CustomFieldValueChange = onChange;
  // Return the HTML of the custom field
  return `
    <custom-field inputValue="${value || ""}"></custom-field>

Once this script has been registered, you can use the customField type in your content-type. Register it as follows:

Configure your custom field in the content-type
  "frontMatter.taxonomy.contentTypes": [{
    "name": "default",
    "pageBundle": false,
    "fields": [
        "title": "Custom field",
        "name": "customField",
        "type": "customField",
        "customType": "customTextField"

Example of a custom field rendering:

Custom field


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