Wordpress Performance Best Practices

---
name: wordpress-performance-best-practices
description: WordPress performance optimization guidelines for plugin, theme, and custom code development. This skill should be used when writing, reviewing, or refactoring WordPress PHP code to ensure optimal performance patterns. Triggers on tasks involving WP_Query, database queries, caching, hooks, REST API, or WordPress theme/plugin development.
license: MIT
metadata:
  author: bartekmis
  version: "1.0.0"
---

# WordPress Performance Best Practices

Comprehensive performance optimization guide for WordPress development, designed for AI agents and LLMs. Contains 34 rules across 8 categories, prioritized by impact to guide code review and generation.

## When to Apply

Reference these guidelines when:
- Writing WordPress plugins or themes
- Working with WP_Query or database operations
- Implementing caching (transients, object cache)
- Optimizing asset loading (scripts, styles)
- Reviewing WordPress code for performance issues
- Working with REST API or AJAX handlers

## Rule Categories by Priority

| Priority | Category | Impact | Prefix |
|----------|----------|--------|--------|
| 1 | Database Optimization | CRITICAL | `db-` |
| 2 | Caching Strategies | CRITICAL | `cache-` |
| 3 | Asset Management | HIGH | `asset-` |
| 4 | Theme Performance | HIGH | `theme-` |
| 5 | Plugin Architecture | MEDIUM-HIGH | `plugin-` |
| 6 | Media Optimization | MEDIUM | `media-` |
| 7 | API and AJAX | MEDIUM | `api-` |
| 8 | Advanced Patterns | LOW-MEDIUM | `advanced-` |

## Quick Reference

### 1. Database Optimization (CRITICAL)

- `db-prepared-statements` - Always use $wpdb->prepare() for queries
- `db-avoid-post-not-in` - Avoid post__not_in, filter in PHP instead
- `db-use-wp-query` - Use WP_Query/get_posts instead of direct DB queries
- `db-limit-query-results` - Never use posts_per_page => -1
- `db-meta-query-indexing` - Optimize meta queries, consider taxonomies
- `db-fields-optimization` - Use fields => 'ids' when only IDs needed

### 2. Caching Strategies (CRITICAL)

- `cache-transients-proper-use` - Use transients for external API calls
- `cache-object-cache` - Use wp_cache_* with cache groups
- `cache-remote-requests` - Always cache wp_remote_get responses
- `cache-invalidation` - Implement precise, event-driven invalidation
- `cache-fragment-caching` - Cache expensive template fragments

### 3. Asset Management (HIGH)

- `asset-proper-enqueue` - Use wp_enqueue_script/style, never hardcode
- `asset-conditional-loading` - Only load assets where needed
- `asset-defer-async` - Use defer/async for non-critical scripts
- `asset-dequeue-unused` - Remove unused plugin assets
- `asset-minification` - Minify assets, use critical CSS

### 4. Theme Performance (HIGH)

- `theme-avoid-queries-in-templates` - Keep queries out of template files
- `theme-template-parts` - Use get_template_part with data passing
- `theme-loop-optimization` - Optimize loops, use meta/term cache priming
- `theme-hooks-placement` - Use appropriate hook priorities

### 5. Plugin Architecture (MEDIUM-HIGH)

- `plugin-conditional-loading` - Load code only when needed
- `plugin-autoloading` - Use PSR-4 autoloading
- `plugin-activation-hooks` - Use activation hooks for setup tasks
- `plugin-hook-removal` - Remove hooks properly with matching priority

### 6. Media Optimization (MEDIUM)

- `media-responsive-images` - Use srcset and sizes attributes
- `media-lazy-loading` - Lazy load below-fold, eager load LCP
- `media-image-sizes` - Define appropriate custom image sizes

### 7. API and AJAX (MEDIUM)

- `api-rest-optimization` - Optimize REST endpoints, add caching headers
- `api-admin-ajax` - Use REST API for frontend, avoid admin-ajax
- `api-nonce-validation` - Implement proper nonce validation

### 8. Advanced Patterns (LOW-MEDIUM)

- `advanced-autoload-optimization` - Keep autoloaded options under 800KB
- `advanced-cron-optimization` - Use system cron, batch long tasks
- `advanced-memory-management` - Process in batches, clean up memory
- `advanced-query-monitor` - Profile before optimizing

## How to Use

Read individual rule files for detailed explanations and code examples:

```
rules/db-prepared-statements.md
rules/cache-transients-proper-use.md
rules/_sections.md
```

Each rule file contains:
- Brief explanation of why it matters
- Incorrect code example with explanation
- Correct code example with explanation
- Additional context and references

## Full Compiled Document

For the complete guide with all rules expanded: `AGENTS.md`