JSON column formatting to preview SharePoint Online file on mouse hover

SharePoint developers can use JSON to format columns, views and customize list form.

Let us look at an example to preview the file content using a hover card, when the user moves the mouse over the file name (or any other field of your choice).

We are going to setup a new column "preview" (single line of text) and apply JSON formatting to this column.

1. Navigate to your list/library.
2. Select the column in view.
3. Click Column settings --> Format this column.

SharePoint JSON column formatting
4. This will open a pane in the right section of screen 'Format preview column'.
5. Copy and paste below JSON in the text box.

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/column-formatting.schema.json",
  "elmType": "img",
  "attributes": {
    "src": "@thumbnail.medium"
  },
  "style": {
    "display": "block",
    "margin": "0 auto",
    "max-height": "100px"
  },
  "customCardProps": {
    "openOnEvent": "hover",
    "isBeakVisible": true,
    "formatter": {
      "elmType": "img",
      "attributes": {
        "src": "@thumbnail.200x400"
      },
      "style": {
        "max-height": "400px"
      }
    }
  }
}

6. Click Preview and make adjustments, if required.
7. Click 'Save' once comfortable with the hover card.