# Add fields to any block

Pure JSON. No templates, no render callbacks.

## Custom fields, zero templates

Create a JSON file, target a block with `name`, and define fields. `set` maps values to classes, styles, data attributes, or any other HTML attribute.

Blockstudio applies output with the WordPress HTML Tag Processor. No templates or render callbacks.

[Extension basics](https://blockstudio.dev/docs/extensions/)

extend-animation.json

```
{
  "name": "core/*",
  "blockstudio": {
    "extend": { "priority": 10 },
    "attributes": [
      {
        "id": "animation",
        "type": "select",
        "allowNull": "None",
        "options": [
          { "value": "fade", "label": "Fade" },
          { "value": "slide", "label": "Slide" }
        ],
        "set": [{
          "attribute": "class",
          "value": "animate-{attributes.animation}"
        }]
      }
    ]
  }
}
```

## Target any block

Extend a block, a list, or a namespace wildcard.

## The set property

Map fields to classes, styles, data attributes, or any HTML attribute.

## Conditional fields

Show fields according to other values with block-style logic.

## Full feature set

All field types, conditional logic, populations, and properties.

## Inspector positioning

Place fields in settings, styles, or advanced tabs.

## Priority ordering

Order multiple extensions targeting the same block.

## No render callbacks

The HTML Tag Processor applies output automatically.

## JSON Schema

Dedicated schema autocomplete and validation.

## Map values to HTML with set

`set` maps values to classes, inline styles, data attributes, or any HTML attribute using dot notation such as `{attributes.fieldId}`.

Access nested object values, apply them conditionally, or output one field to multiple attributes.

A field that returns several values applies `set` to each one. Classes and styles add up; for any other attribute, `"join": true` writes every value, separated by spaces, instead of keeping the last.

[The set property](https://blockstudio.dev/docs/extensions/#attributes)

extend-color.json

```
{
  "name": "core/heading",
  "blockstudio": {
    "extend": { "priority": 10 },
    "attributes": [
      {
        "id": "customColor",
        "type": "select",
        "returnFormat": "both",
        "options": [
          { "value": "#f00", "label": "Red" },
          { "value": "#00f", "label": "Blue" }
        ],
        "set": [
          { "attribute": "style", "value": "color: {attributes.customColor.value}" },
          { "attribute": "data-color", "value": "{attributes.customColor.label}" },
          { "attribute": "class", "value": "has-custom-color" }
        ]
      }
    ]
  }
}
```

## Target one block or thousands

Target one name such as `"core/paragraph"`, an array of names, or an entire namespace with `"core/*"`.

Multiple JSON extensions may target the same block. Priority controls their inspector order.

A top-level `exclude` list skips blocks that `name` would match, using the same exact and wildcard matching. An excluded block gets neither the fields nor their output.

[Targeting blocks](https://blockstudio.dev/docs/extensions/)

extend-animation.json

```
{
  "name": "core/*",
  "blockstudio": {
    "extend": { "priority": 10 },
    "attributes": [
      {
        "id": "animation",
        "type": "select",
        "options": [
          { "value": "fade", "label": "Fade" },
          { "value": "slide", "label": "Slide" }
        ]
      }
    ]
  }
}
```

## Exclude blocks

Skip single blocks or whole prefixes that a wildcard would otherwise match.

## Joined values

Write every selected value of a multi-value field into one attribute.

## Attributes field

An attributes field writes its name and value pairs onto the block without a set rule.

## Inspect from PHP

bs_block_extension_fields() returns the fields every matching extension adds to a block, core and third-party blocks included.

Plus

## The official extension kit

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- 500+ site templates
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- Lifetime updates
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[Get Plus](https://blockstudio.dev/plus/)