WP Performance Review

When to use

Use this skill when:

• Reviewing PR/code for WordPress theme or plugin
• User reports slow page loads, timeouts, or 500 errors
• Auditing before high-traffic event (launch, sale, viral moment)
• Optimizing WP_Query or database operations
• Investigating memory exhaustion or DB locks

Inputs required

• Files or directories to review.
• Context: dev/staging/prod environment.
• Any constraints: read-only access, no plugin installs.
• Symptoms: slow TTFB, specific URL, admin vs frontend.

Procedure

0) Identify scope and file types

1. Identify file type and apply relevant checks
2. Note hosting environment (managed, self-hosted, shared)
3. Determine if this is admin-only or frontend code

1) Scan for critical patterns first

Run quick detection scans:

# Unbounded queries - CRITICAL
grep -rn "posts_per_page.*-1\|numberposts.*-1" .

# query_posts - CRITICAL
grep -rn "query_posts\s*(" .

# Session start - CRITICAL (bypasses page cache)
grep -rn "session_start\s*(" .

# Polling patterns - CRITICAL (self-DDoS)
grep -rn "setInterval.*fetch\|setInterval.*ajax" .

Read:

• references/anti-patterns.md

2) Check warnings (inefficient but not catastrophic)

# DB writes on frontend
grep -rn "update_option\|add_option" . | grep -v "admin\|activate"

# Uncached expensive functions
grep -rn "url_to_postid\|attachment_url_to_postid" .

# External HTTP without caching
grep -rn "wp_remote_get\|wp_remote_post" .

# Cache bypass
grep -rn "cache_results.*false" .

3) Check file-type specific patterns

WP_Query / Database Code:

• Missing posts_per_page argument
• meta_query with value comparisons (unindexed)
• post__not_in with large arrays
• LIKE '%term%' (leading wildcard)

AJAX Handlers:

• POST method for read operations (bypasses cache)
• Missing nonce verification

Template Files:

• Database queries inside loops (N+1)
• wp_remote_get in templates

Read:

• references/file-type-checks.md

4) Report findings with severity

Structure findings as:

## Performance Review: [filename]

### Critical Issues
- **Line X**: [Issue] - [Explanation] - [Fix]

### Warnings
- **Line X**: [Issue] - [Explanation] - [Fix]

### Recommendations
- [Optimization opportunities]

Read:

• references/output-format.md

Verification

• All critical issues have been identified
• Line numbers are accurate
• Fixes are actionable and WordPress-specific
• Context is considered (admin vs frontend)

Failure modes / debugging

• False positive on admin-only code:
  • Check context - admin, CLI, cron are lower risk
• Missing session_start() in plugin:
  • Always grep across ALL code including plugins
• Ignoring JS polling patterns:
  • Review .js files for setInterval + fetch

Read:

• references/common-mistakes.md

WordPress 6.9 Performance Improvements

Be aware of these 6.9 changes when profiling:

On-demand CSS for classic themes:

• Classic themes now get on-demand CSS loading (previously only block themes)
• Reduces CSS payload by 30-65% by only loading styles for blocks actually used
• If profiling a classic theme, this should already be helping

Block themes with no render-blocking resources:

• Block themes without custom stylesheets (like Twenty Twenty-Three/Four) can now load with zero render-blocking CSS
• Styles come from global styles (theme.json) and separate block styles, all inlined
• Significantly improves LCP (Largest Contentful Paint)

Inline CSS limit increased:

• The threshold for inlining small stylesheets has been raised
• Reduces render-blocking resources

WP-CLI Profiling Commands

If WP-CLI is available, use these for deep profiling:

# See where time goes (bootstrap/main_query/template)
wp profile stage --url=https://example.com/page/

# Find slow hooks/callbacks
wp profile hook --url=https://example.com/page/

# Profile specific code path
wp profile eval 'do_action("init");'

# Run health checks
wp doctor check

Query Monitor Headless Usage

For backend-only debugging, Query Monitor works via REST API:

1. Authenticate (nonce or Application Password)
2. Request with ?_envelope parameter
3. Inspect x-qm-* headers or qm property in response

Escalation

• If production and no explicit approval, do NOT: install plugins, enable SAVEQUERIES, run load tests, or flush caches during traffic
• For system-level profiling (APM, PHP profilers), coordinate with ops/hosting

Consult:

• WordPress Performance Team Handbook
• Query Monitor Plugin
• WP 6.9 Frontend Performance Field Guide