What Speed Optimizer does on your site
Speed Optimizer, formerly SG Optimizer, is the performance plugin from the web host SiteGround. It is free, with no paid tier, and since version 7.0 it installs on any host. Its settings are split into four menus: Caching, Environment (HTTPS, Heartbeat, database maintenance), Frontend (minification, combination and deferral of scripts, fonts) and Media (compression, WebP, lazy loading), plus a speed test powered by Google PageSpeed.
The deciding factor: several key features only work on SiteGround servers. The official documentation says so plainly for Dynamic Caching (a full-page cache run by NGINX), for Memcached, for image compression and for WebP images. Elsewhere you still get File-Based Caching (static HTML copies in wp-content/cache/sgo-cache/), code optimizations and lazy loading. On another host, the plugin also shows two settings that SiteGround already handles at server level: GZIP compression and browser caching.
Minified or combined CSS and JavaScript files are written to wp-content/uploads/siteground-optimizer-assets/. The plugin also ships WP-CLI commands (wp sg purge, wp sg status...) and optional technical data collection, which you control from the admin.
Which sites Speed Optimizer suits best
- Sites hosted at SiteGround: the plugin drives the server's dynamic cache, purges it at the right time and unlocks Memcached and image compression with no third-party service.
- Blogs and brochure sites that want few knobs to turn: each menu flags its recommended optimizations, and the dashboard counts the ones still waiting.
- Agencies running several SiteGround sites: WP-CLI commands and multisite options let you purge or configure without opening the interface.
Off SiteGround, the case gets much weaker: you would only get a file cache and code optimizations, with no image compression or WebP. A plugin built for any server, such as WP Rocket, or your host's own server cache is often the better fit (see our hosting and cache compatibility page). Never run two page caches at once.
Speed Optimizer strengths and limits
Strengths
- Built into SiteGround servers. The NGINX dynamic cache is on by default, and the plugin purges it smartly after every content change.
- Completely free. No license and no feature locked behind a subscription.
- Simple interface. Clear toggles, flagged recommendations and a cache status test for any given URL.
- Fine-grained exclusions. URLs with a
*wildcard, post types, and scripts excluded from minification, combination or deferral.
Limits
- Key features are SiteGround-only. Dynamic Caching, Memcached, image compression and WebP work only with this host.
- No critical CSS. Unlike some optimization plugins, it neither generates critical CSS nor removes unused CSS.
- Combination and deferral carry risk. The documentation warns they can break scripts that need a specific execution order.
- Thin changelog. Security fixes get a single line ("Security improvements") with no description of the flaw.
The Speed Optimizer settings we recommend
Turn on one setting at a time, purge the cache, then test in a private window. Judge the effect on the Core Web Vitals of your real pages, not on a single score.
| Setting | Recommended value | Why |
|---|---|---|
| Dynamic Caching Speed Optimizer > Caching | On (SiteGround only) | This is the server's page cache and the plugin's main gain. |
| File-Based Caching Speed Optimizer > Caching | On outside SiteGround, if no other page cache is active | It is the only page cache available elsewhere; at SiteGround it requires Dynamic Caching. |
| Automatic Purge Speed Optimizer > Caching | On; REST API option off unless needed | SiteGround strongly recommends it: without it, visitors see stale versions of your pages. |
| Logged-in users cache Caching > File-Based Caching > Configure | Off (default) | One cache per user makes the cache grow; test it only on a membership site. |
| Minify CSS Files, Minify JavaScript Files, Minify the HTML Output Speed Optimizer > Frontend | On, after checking your pages | Real gain, low risk; exclude a file if it causes trouble. |
| Combine JavaScript Files and Defer Render-blocking JavaScript Speed Optimizer > Frontend | Off, unless the gain is measured and every page type tested | They can break scripts that need a set execution order: forms, menus, cart, cookie banner. |
| Lazy Load Media Speed Optimizer > Media | On, with the above-the-fold image excluded by its CSS class | Some sliders stop working: check them and exclude them if needed. |
| WordPress Heartbeat Optimization Speed Optimizer > Environment | "Posts and Pages" at 120 seconds | The value the plugin suggests: fewer requests while keeping autosave. |
| HTTPS Enforce Speed Optimizer > Environment | On only with a valid certificate | It adds a rule to .htaccess and logs you out of the admin. |
- Check a page with "Test URL Caching Status" (Speed Optimizer > Caching), then an excluded URL.
- At SiteGround, turn Memcached on in Site Tools (Speed > Caching) before enabling it in the plugin, or it cannot connect.
- After each optimization, test a form, the mobile menu, the cart and the cookie banner.
- Make sure no other page cache plugin is active, then turn on auto-updates for Speed Optimizer.
Speed Optimizer vulnerabilities and the version to run
- CVE-2019-25217, fixed in 5.0.13: a misapplied access check on a REST API route allowed including and executing files already on the server.
- CVE-2024-32532, fixed in 7.5.0: a missing authorization check let anyone purge the cache without logging in.
- CVE-2026-3220, fixed in 7.7.9: an unauthenticated stored XSS flaw in HTML minification, shared with Autoptimize and Clearfy Cache.
The changelog also lists "Security improvements" in several 2026 releases, including 7.8.5, which fixes two issues reported by a researcher. Always run the latest version and turn on auto-updates. WP Masquerade Pro renames the plugin's folder, its tag IDs and its generated-files folder, which makes it harder for bots to spot, but SiteGround's cache headers stay visible and nothing replaces updating.
What WP Masquerade hides for Speed Optimizer
Free version Handled by the free version of WP Masquerade
Speed Optimizer is one of the 50 most used plugins known to the free version. Pro goes further by renaming its files.
Free version
Nothing to remove
With Pro
- folder name
- tag IDs
- generated-file folders
Still visible
- server or cache headers
X-Cache-Enabled, X-Proxy-Cache
These traces stay because the plugin needs them to work (scripts, styles, cookies) or because they come from the server.
Speed Optimizer FAQ
Does Speed Optimizer work with hosts other than SiteGround?
Yes since version 7.0, but only partly: file caching, minification, combination, script deferral and lazy loading work; Dynamic Caching, Memcached, image compression and WebP remain SiteGround-only.
Do SiteGround customers need to install Speed Optimizer?
The dynamic cache runs at server level, but it is the plugin that purges it automatically when you publish or edit content. Without it or another way to purge, stale pages can stay cached.
Can I use it alongside WP Rocket or another caching plugin?
Not for page caching: only one should be active. For minification and script deferral, turn each feature on in just one of the two plugins.
My site looks broken after an optimization. What should I do?
Turn off the last setting you changed and purge the cache. If a single script is the culprit, add it to the matching exclusion list, such as "Exclude from Deferral of Render-blocking JS".