How to create category attribute programmatically in Magento2

From Magento 2.1 and upper Version, You can also refer blog for create attribute programmatically in detais by, Create Custom category attribute in Magento 2

You have to just below code inside

For Magento Version 2.1.*

app/code/{Packagename}/{Modulename}/Setup/InstallData.php

<?php
namespace {Packagename}\{Modulename}\Setup;

use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;
use Magento\Catalog\Setup\CategorySetupFactory; 

class InstallData implements InstallDataInterface
{
    /**
    * Category setup factory
    *
    * @var CategorySetupFactory
    */
    private $categorySetupFactory;
    /**
    * Init
    *
    * @param CategorySetupFactory $categorySetupFactory
    */
    public function __construct(CategorySetupFactory $categorySetupFactory)
    {
         $this->categorySetupFactory = $categorySetupFactory;
    }

    public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {
         $installer = $setup;
         $installer->startSetup();
         $categorySetup = $this->categorySetupFactory->create(['setup' => $setup]);
         $entityTypeId = $categorySetup->getEntityTypeId(\Magento\Catalog\Model\Category::ENTITY);
         $attributeSetId = $categorySetup->getDefaultAttributeSetId($entityTypeId);

         $categorySetup->addAttribute(
         \Magento\Catalog\Model\Category::ENTITY, 'custom_attribute', [
            'type' => 'varchar',
            'label' => 'Custom Attribute Description',
            'input' => 'textarea',
            'required' => false,
            'sort_order' => 100,
            'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_STORE,
            'group' => 'General Information',
            'is_used_in_grid' => true,
            'is_visible_in_grid' => false,
            'is_filterable_in_grid' => true,
         ]
         );
         $installer->endSetup();
    }
}

app/code/{Packagename}/{Modulename}/view/adminhtml/ui_component/category_form.xml

<?xml version="1.0" encoding="UTF-8"?>
<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">
  <fieldset name="general"> 
     <field name="custom_attribute">
        <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="sortOrder" xsi:type="number">50</item>
                    <item name="dataType" xsi:type="string">string</item>
                    <item name="formElement" xsi:type="string">input</item>
                    <item name="label" xsi:type="string" translate="true">Custom Attribute Name</item>
                </item>
        </argument>
    </field>  
  </fieldset>
</form>

This is older version of Magento,

For Magento Version 2.0.*

Set category attribute like below,

app/code/Vendor/Categoryattr/Setup/InstallData.php file,

<?php
/**
 * Copyright © 2015 Magento. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Vendor\CategoryAttribute\Setup;

use Magento\Eav\Setup\EavSetup;
use Magento\Eav\Setup\EavSetupFactory;
use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;


class InstallData implements InstallDataInterface
{
    private $eavSetupFactory; 
    /**
     * Init
     *
     * @param EavSetupFactory $eavSetupFactory
     */
    public function __construct(EavSetupFactory $eavSetupFactory)
    {
        $this->eavSetupFactory = $eavSetupFactory;
    }

    /**
     * {@inheritdoc}
     * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
     */
    public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {
        /** @var EavSetup $eavSetup */
        $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);
        /**
         * Add attributes to the eav/attribute
         */ 
        $eavSetup->addAttribute(
            \Magento\Catalog\Model\Category::ENTITY,
            'custom_attribute',
                      [
                        'type' => 'varchar',
                        'label' => 'Custom Attribute Description',
                        'input' => 'textarea',
                        'required' => false,
                        'sort_order' => 100,
                        'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_STORE,
                        'group' => 'General Information',
                        'is_used_in_grid' => true,
                        'is_visible_in_grid' => false,
                        'is_filterable_in_grid' => true,
            ]
        );


    }
}

remove var/generation folder and run command,

php bin/magento setup:upgrade to working inside category.

As of magento 2.1 you will also need to create a UI components before the field will show up in admin.

Create:

app/code/Vendor/Categoryattr/view/adminhtml/ui_component/category_form.xml

<?xml version="1.0" encoding="UTF-8"?>
<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">

    <fieldset name="custom_tab">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="label" xsi:type="string" translate="true">Custom Tab Name</item>
                <item name="collapsible" xsi:type="boolean">true</item>
                <item name="sortOrder" xsi:type="number">12</item>
            </item>
        </argument>
        <field name="custom_attribute">
            <argument name="data" xsi:type="array">
                <item name="config" xsi:type="array">
                    <item name="class" xsi:type="string">Magento\Catalog\Ui\Component\Category\Form\Element\Wysiwyg</item>
                    <item name="formElement" xsi:type="string">wysiwyg</item>
                    <item name="wysiwygConfigData" xsi:type="array">
                        <item name="settings" xsi:type="array">
                            <item name="theme_advanced_buttons1" xsi:type="string">bold,italic,|,justifyleft,justifycenter,justifyright,|,fontselect,fontsizeselect,|,forecolor,backcolor,|,link,unlink,image,|,bullist,numlist,|,code</item>
                            <item name="theme_advanced_buttons2" xsi:type="boolean">false</item>
                            <item name="theme_advanced_buttons3" xsi:type="boolean">false</item>
                            <item name="theme_advanced_buttons4" xsi:type="boolean">false</item>
                            <item name="theme_advanced_statusbar_location" xsi:type="boolean">false</item>
                        </item>
                        <item name="files_browser_window_url" xsi:type="boolean">false</item>
                        <item name="height" xsi:type="string">100px</item>
                        <item name="toggle_button" xsi:type="boolean">false</item>
                        <item name="add_variables" xsi:type="boolean">false</item>
                        <item name="add_widgets" xsi:type="boolean">false</item>
                        <item name="add_images" xsi:type="boolean">false</item>
                    </item>
                    <item name="template" xsi:type="string">ui/form/field</item>
                    <item name="source" xsi:type="string">category</item>
                    <item name="wysiwyg" xsi:type="boolean">true</item>
                    <item name="dataScope" xsi:type="string">description</item>
                    <item name="sortOrder" xsi:type="number">50</item>
                    <item name="rows" xsi:type="number">8</item>
                </item>
            </argument>
        </field>
    </fieldset>
</form>