Inefficient REST API usage

Problem Summary

WordPress REST API can be inefficient when endpoints aren’t optimized—making too many requests, returning excessive data, or lacking caching. This creates unnecessary server load and slower client-side performance.

Performance Impact

• Increased server load: Each API call triggers database queries
• Larger response payloads: Returning more data than needed
• No caching: Repeated requests hit the database every time
• Client-side delays: JavaScript waits for API responses

How to Detect

1. Query Monitor plugin: Shows REST API queries and timing
2. Chrome DevTools Network: Filter by /wp-json/ to see API calls
3. Server logs: High volume of REST API requests
4. PageSpeed Insights: May flag slow API responses

Solutions

1. Limit Returned Fields

// Instead of /wp-json/wp/v2/posts// Use ?_fields=id,title,excerpt,featured_media

2. Add Caching to Endpoints

<?php
add_action('rest_api_init', function() {  header('Cache-Control: public, max-age=3600');});

3. Use Transients for Expensive Queries

 = get_transient('my_api_data');if (false === ) {   = get_posts(['numberposts' => 10]);  set_transient('my_api_data', , HOUR_IN_SECONDS);}return ;

4. Optimize Query Parameters

// Instead of default per_page=10'posts_per_page' => 5,'orderby' => 'date','order' => 'DESC'

5. Disable Unneeded Endpoints

<?php
add_filter('rest_endpoints', function() {  unset(['/wp/v2/users']);  unset(['/wp/v2/comments']);  return ;});

Further Reading

• WordPress REST API Handbook
• WPGraphQL alternative