Developer Reference

Filters and hooks for extending Fluid Design System for Elementor.

Custom Presets

Add preset groups programmatically.

arts/fluid_design_system/custom_presets

add_filter('arts/fluid_design_system/custom_presets', function($groups) {
    $groups[] = [
        'name' => 'My Theme Tokens',
        'description' => 'Design tokens for My Theme',
        'value' => [
            [
                'id' => 'theme-space-xs',
                'title' => 'XS Space',
                'value' => 'var(--theme-space-xs)',
            ],
            [
                'id' => 'theme-space-s',
                'title' => 'S Space',
                'value' => 'var(--theme-space-s)',
                'display_value' => '1rem', // Optional: show instead of CSS var
            ],
        ],
    ];
    return $groups;
});

arts/fluid_design_system/registered_groups

Register editable preset groups in code. Each group gets its own section in Site Settings, and its presets are stored in the Kit under fluid_custom_{id}_presets, so they travel with a Kit export/import while the group itself comes from your code on every install.

add_filter('arts/fluid_design_system/registered_groups', function($groups) {
    $groups['mytheme_layout'] = [
        'name' => 'Layout',
        'description' => '', // Optional
        'order' => 1,        // Optional: position among custom groups
    ];
    return $groups;
});

Keys must be sanitize_key()-clean (lowercase letters, digits, _, -). Registered groups can be reordered and their presets edited like any other, but they can't be renamed or deleted in the admin or through the MCP tools.

Control Eligibility

arts/fluid_design_system/controls/is_eligible_for_fluid_unit

Determine if a control should support fluid units.

add_filter('arts/fluid_design_system/controls/is_eligible_for_fluid_unit', function($eligible, $control) {
    if ($control['type'] === 'my_custom_slider') {
        return true;
    }
    return $eligible;
}, 10, 2);

arts/fluid_design_system/controls/eligible_for_fluid_unit

Filter the complete list of eligible controls.

add_filter('arts/fluid_design_system/controls/eligible_for_fluid_unit', function($eligible_controls, $controls) {
    if (isset($controls['my_custom_control'])) {
        $eligible_controls['my_custom_control'] = $controls['my_custom_control'];
    }
    return $eligible_controls;
}, 10, 2);

arts/fluid_design_system/controls/eligible_types_for_selector_modification

Add control types for selector modification.

add_filter('arts/fluid_design_system/controls/eligible_types_for_selector_modification', function($types) {
    $types[] = 'my_custom_slider';
    return $types;
});

CSS Customization

arts/fluid_design_system/controls/modified_css_property

Modify CSS property output.

add_filter('arts/fluid_design_system/controls/modified_css_property', function($css, $property, $selector, $control, $value) {
    if ($control['name'] === 'my_special_control') {
        $css .= '; transform: scale(var(--scale-factor))';
    }
    return $css;
}, 10, 5);

arts/fluid_design_system/css/var_preset

Customize CSS variable names.

add_filter('arts/fluid_design_system/css/var_preset', function($var_name, $id) {
    if (strpos($id, 'special-') === 0) {
        return '--custom-' . $id;
    }
    return $var_name;
}, 10, 2);

arts/fluid_design_system/css/clamp_formula

Customize the clamp formula.

add_filter('arts/fluid_design_system/css/clamp_formula', function($formula, $parts) {
    // Use custom viewport calculation
    return "clamp({$parts['min_size']}, 5vw, {$parts['max_size']})";
}, 10, 2);

Actions

arts/fluid_design_system/controls/after_add_fluid_unit

Fired after fluid unit is added to controls.

add_action('arts/fluid_design_system/controls/after_add_fluid_unit', function($element, $section_id, $args, $units) {
    if ($element->get_name() === 'my-widget' && $section_id === 'style_section') {
        $element->update_control('custom_padding', [
            'size_units' => ['px', '%', 'em', 'rem', 'fluid'],
        ]);
    }
}, 10, 4);

AI Agents (MCP)

The plugin registers a dedicated MCP server that lets AI agents manage presets and preset groups programmatically.

Requirements

• WordPress 6.9+ (ships with the Abilities API)
• MCP Adapter plugin installed and active

Available Tools

Tool	Description
fluid/list-preset-groups	Lists all groups with metadata
fluid/get-preset-group	Returns a group and its presets
fluid/create-preset-group	Creates a custom group
fluid/rename-preset-group	Renames a custom group
fluid/delete-preset-group	Deletes a custom group and its presets
fluid/list-presets	Lists presets across all or a specific group
fluid/get-preset	Returns a single preset by ID
fluid/create-preset	Creates a preset (plugin computes the clamp formula)
fluid/update-preset	Renames a preset or moves it to another group
fluid/delete-preset	Removes a preset
fluid/move-preset-to-group	Moves a preset between groups atomically

Read tools require edit_posts, write tools require manage_options.

Connecting via WP-CLI

# List available MCP servers
wp mcp-adapter list

# Start STDIO session
echo '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}' | \
  wp mcp-adapter serve --user=admin --server=fluid-design-system

Connecting Claude Code

Create a .mcp.json in your project root:

{
  "mcpServers": {
    "fluid-design-system": {
      "command": "wp",
      "args": [
        "--path=/path/to/wordpress",
        "mcp-adapter",
        "serve",
        "--server=fluid-design-system",
        "--user=admin"
      ]
    }
  }
}

Adjust --path and --user for your environment. If using Local by Flywheel, you'll need the full PHP binary path and a -d mysqli.default_socket=... argument.

Logging

Every tool execution fires the arts/fluid_design_system/ability_executed action:

add_action('arts/fluid_design_system/ability_executed', function($log_entry) {
    // $log_entry contains: ability, user_id, timestamp, input, success
    error_log('Fluid DS: ' . $log_entry['ability'] . ' by user ' . $log_entry['user_id']);
});

When WP_DEBUG_LOG is enabled, executions are also written to the WordPress debug log automatically.

Complete Example

Add fluid support to a custom widget:

function my_theme_add_fluid_support() {
    // 1. Make dimension controls eligible
    add_filter('arts/fluid_design_system/controls/is_eligible_for_fluid_unit', function($eligible, $control) {
        if ($control['parent'] === 'my_widget' && $control['type'] === 'dimensions') {
            return true;
        }
        return $eligible;
    }, 10, 2);

    // 2. Modify CSS output
    add_filter('arts/fluid_design_system/controls/modified_css_property', function($css, $property, $selector, $control, $value) {
        if (strpos($selector, '.my-widget') !== false) {
            return $css . '; transition: all 0.3s ease';
        }
        return $css;
    }, 10, 5);

    // 3. Manually add fluid unit to controls
    add_action('arts/fluid_design_system/controls/after_add_fluid_unit', function($element, $section_id, $args, $units) {
        if ($element->get_name() === 'my_widget') {
            $element->update_control('custom_padding', [
                'size_units' => ['px', '%', 'em', 'rem', 'fluid'],
            ]);
        }
    }, 10, 4);
}
add_action('init', 'my_theme_add_fluid_support');

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