Wp Performance

1---
2name: wp-performance
3description: "Use when investigating or improving WordPress performance (backend-only agent): profiling and measurement (WP-CLI profile/doctor, Server-Timing, Query Monitor via REST headers), database/query optimization, autoloaded options, object caching, cron, HTTP API calls, and safe verification."
4compatibility: "Targets WordPress 6.9+ (PHP 7.2.24+). Backend-only agent; prefers WP-CLI (doctor/profile) when available."
5---
6 
7# WP Performance (backend-only)
8 
9## When to use
10 
11Use this skill when:
12 
13- a WordPress site/page/endpoint is slow (frontend TTFB, admin, REST, WP-Cron)
14- you need a profiling plan and tooling recommendations (WP-CLI profile/doctor, Query Monitor, Xdebug/XHProf, APMs)
15- you’re optimizing DB queries, autoloaded options, object caching, cron tasks, or remote HTTP calls
16 
17This skill assumes the agent cannot use a browser UI. Prefer WP-CLI, logs, and HTTP requests.
18 
19## Inputs required
20 
21- Environment and safety: dev/staging/prod, any restrictions (no writes, no plugin installs).
22- How to target the install:
23  - WP root `--path=<path>`
24  - (multisite/site targeting) `--url=<url>`
25- The performance symptom and scope:
26  - which URL/REST route/admin screen
27  - when it happens (always vs sporadic; logged-in vs logged-out)
28 
29## Procedure
30 
31### 0) Guardrails: measure first, avoid risky ops
32 
331. Confirm whether you may run write operations (plugin installs, config changes, cache flush).
342. Pick a reproducible target (URL or REST route) and capture a baseline:
35   - TTFB/time with `curl` if possible
36   - WP-CLI profiling if available
37 
38Read:
39- `references/measurement.md`
40 
41### 1) Generate a backend-only performance report (deterministic)
42 
43Run:
44 
45- `node skills/wp-performance/scripts/perf_inspect.mjs --path=<path> [--url=<url>]`
46 
47This detects:
48 
49- WP-CLI availability and core version
50- whether `wp doctor` / `wp profile` are available
51- autoloaded options size (if possible)
52- object-cache drop-in presence
53 
54### 2) Fast wins: run diagnostics before deep profiling
55 
56If you have WP-CLI access, prefer:
57 
58- `wp doctor check`
59 
60It catches common production foot-guns (autoload bloat, SAVEQUERIES/WP_DEBUG, plugin counts, updates).
61 
62Read:
63- `references/wp-cli-doctor.md`
64 
65### 3) Deep profiling (no browser required)
66 
67Preferred order:
68 
691. `wp profile stage` to see where time goes (bootstrap/main_query/template).
702. `wp profile hook` (optionally with `--url=`) to find slow hooks/callbacks.
713. `wp profile eval` for targeted code paths.
72 
73Read:
74- `references/wp-cli-profile.md`
75 
76### 4) Query Monitor (backend-only usage)
77 
78Query Monitor is normally UI-driven, but it can be used headlessly via REST API response headers and `_envelope` responses:
79 
80- Authenticate (nonce or Application Password).
81- Request REST responses and inspect headers (`x-qm-*`) and/or the `qm` property when using `?_envelope`.
82 
83Read:
84- `references/query-monitor-headless.md`
85 
86### 5) Fix by category (choose the dominant bottleneck)
87 
88Use the profile output to pick *one* primary bottleneck category:
89 
90- **DB queries** → reduce query count, fix N+1 patterns, improve indexes, avoid expensive meta queries.
91  - `references/database.md`
92- **Autoloaded options** → identify the biggest autoloaded options and stop autoloading large blobs.
93  - `references/autoload-options.md`
94- **Object cache misses** → introduce caching or fix cache key/group usage; add persistent object cache where appropriate.
95  - `references/object-cache.md`
96- **Remote HTTP calls** → add timeouts, caching, batching; avoid calling remote APIs on every request.
97  - `references/http-api.md`
98- **Cron** → reduce due-now spikes, de-duplicate events, move heavy tasks out of request paths.
99  - `references/cron.md`
100 
101### 6) Verify (repeat the same measurement)
102 
103- Re-run the same `wp profile` / `wp doctor` / REST request.
104- Confirm the performance delta and that behavior is unchanged.
105- If the fix is risky, ship behind a feature flag or staged rollout when possible.
106 
107## WordPress 6.9 performance improvements
108 
109Be aware of these 6.9 changes when profiling:
110 
111**On-demand CSS for classic themes:**
112- Classic themes now get on-demand CSS loading (previously only block themes had this).
113- Reduces CSS payload by 30-65% by only loading styles for blocks actually used on the page.
114- If you're profiling a classic theme, this should already be helping.
115 
116**Block themes with no render-blocking resources:**
117- Block themes that don't define custom stylesheets (like Twenty Twenty-Three/Four) can now load with zero render-blocking CSS.
118- Styles come from global styles (theme.json) and separate block styles, all inlined.
119- This significantly improves LCP (Largest Contentful Paint).
120 
121**Inline CSS limit increased:**
122- The threshold for inlining small stylesheets has been raised, reducing render-blocking resources.
123 
124Reference: https://make.wordpress.org/core/2025/11/18/wordpress-6-9-frontend-performance-field-guide/
125 
126## Verification
127 
128- Baseline vs after numbers are captured (same environment, same URL/route).
129- `wp doctor check` is clean (or improved) when applicable.
130- No new PHP errors or warnings in logs.
131- No cache flush is required for correctness (cache flush should be last resort).
132 
133## Failure modes / debugging
134 
135- “No change” after code changes:
136  - you measured a different URL/site (`--url` mismatch), caches masked results, or opcode cache is stale
137- Profiling data is noisy:
138  - eliminate background tasks, test with warmed caches, run multiple samples
139- `SAVEQUERIES`/Query Monitor causes overhead:
140  - don’t run in production unless explicitly approved
141 
142## Escalation
143 
144- If this is production and you don’t have explicit approval, do not:
145  - install plugins, enable `SAVEQUERIES`, run load tests, or flush caches during traffic
146- If you need system-level profiling (APM, PHP profiler extensions), coordinate with ops/hosting.
147