Magento – where to find Magento 2 API docs

What I wanted I achieved by this endpoint /rest/V1/products/attributes

and using this search Criteria

$params= ['searchCriteria' => 
               ['filterGroups' => 
                        [0 => [
                             'filters' => [ 
                                         0 => [ 
                                            'field' => 'attribute_id', 
                                            'value' => 1, 
                                            'condition_type' => 'gteq' 
]
        ]]]]];

I have added stock_item in Category List Product details Rest API. Update ExtensionPool data of Magento\Catalog\Api\Data\ProductInterface and add stock_item data provider.

File path: magento\app\code\Vendor\StockitemApi\registration.php

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

use \Magento\Framework\Component\ComponentRegistrar;

ComponentRegistrar::register(ComponentRegistrar::MODULE, 'Vendor_StockitemApi', __DIR__);

File path: magento\app\code\Vendor\StockitemApi\etc\module.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Vendor_StockitemApi" >
    </module>
</config>

File path: magento\app\code\Vendor\StockitemApi\etc\di.xml

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Framework\EntityManager\Operation\ExtensionPool">
        <arguments>
            <argument name="extensionActions" xsi:type="array">
                <item name="Magento\Catalog\Api\Data\ProductInterface" xsi:type="array">
                    <item name="read" xsi:type="array">
                        <item name="stock_item" xsi:type="string">Vendor\StockitemApi\Model\ReadHandler</item>
                    </item>
                </item>
            </argument>
        </arguments>
    </type>
</config>

File path: magento\app\code\Vendor\StockitemApi\Model\ReadHandler.php

<?php

namespace Vendor\StockitemApi\Model;


class ReadHandler implements \Magento\Framework\EntityManager\Operation\ExtensionInterface
{

    /**
     * @var \Magento\CatalogInventory\Api\StockRegistryInterface
     */
    private $stockRegistry;

    public function __construct(
    \Magento\CatalogInventory\Api\StockRegistryInterface $stockRegistry     
    ) {

        $this->stockRegistry = $stockRegistry;
    }
    /**
     * Magento\CatalogInventory\Api\Data\StockItemInterface
     * @param type $product
     * @param type $arguments
     */
    public function execute($product, $arguments = [])
    {
        if ($product->getExtensionAttributes()->getStockItem() !== null) {
            return $product;
        }

        $stockItem =$this->stockRegistry->getStockItem($product->getId());
        $extensionAttributes = $product->getExtensionAttributes();
        $extensionAttributes->setStockItem($stockItem);
        $product->setExtensionAttributes($extensionAttributes);

        return $product;        
    }

}