Multisite

What is per site, what is shared

Nothing is applied network-wide by default. Changing a setting on one site changes that site only.

The runtime settings snapshot, per site

The drop-in serves cached pages before WordPress loads, so it cannot read the database. Instead it reads a small snapshot file that the plugin writes on activation and on every settings save.

On a network each site writes its own snapshot, wp-content/cache/cachingout/runtime-config-<blog id>.php. The shared runtime-config.php follows the main site and carries the list of sites the drop-in uses to work out which site a request belongs to. A request for a subsite is served with that subsite's cache lifespan, cookie exclusions and query-string allow-list, not with whichever site saved its settings last.

A site that has never saved its settings has no snapshot of its own and is served with the shared one until it does. The Network Admin screen says so next to the site, and the site's own Filesystem Check reports it under "Runtime settings snapshot". Saving any settings page on that site once fixes it.

Purging a site's cache leaves the snapshots in place, and a purge on one site never clears another: since 0.1.20 every purge the plugin triggers on a site (theme switch, menu or widget change, term edit, plugin activation, settings save, the admin-bar Purge, wp cachingout purge) clears that site only. The whole network is cleared only by Purge every site in Network Admin.

Where the network screens are

Network administrators (the manage_network_options capability) get a Caching Out entry in the Network Admin menu (My Sites > Network Admin > Caching Out, or /wp-admin/network/admin.php?page=cachingout-network). It is not a tab inside a site's own Caching Out settings, because those settings belong to one site; the network screens sit where WordPress puts everything that spans sites (Sites, Themes, Plugins at network level). The screens use the same look as the plugin's own settings pages and have two tabs: Sites and Apply settings to sites.

Network Admin > Caching Out > Sites

The Sites tab lists every site in the network, 200 per page, with:

Above the table, Purge every site clears every site's cached pages at once. It is the only action anywhere in the plugin that clears the whole network: a purge triggered on one site (a theme switch, a menu change, a settings save, the admin-bar Purge) clears that site only.

What each button does, and how to undo it

Network Admin > Caching Out > Apply settings to sites

Apply settings to sites copies one settings section to the sites you choose, in three steps. The first two write nothing.

Step 1: choose

Pick three things:

1. Copy from: a site in the network, or Plugin defaults (the values a fresh site starts with).
2. Section: one of Cache, Browser Caching, Media, File Optimization (including every Unused CSS/JS rule), or Preload. One section at a time, so the preview stays readable; everything outside the section stays exactly as each site has it. The screen lists what each section contains.
3. Apply to: tick the target sites. Nothing is ticked by default and nothing is ever applied network-wide on its own. Ticking the source site itself is harmless; it shows as "no change".

Not offered, on purpose: Licence (per site, see below), Insights consent (each site opts in for itself) and Database cleanup (it has its own per-site preview before anything is deleted).

Clicking Preview changes reads the source once. Its own settings are never changed by this flow.

Step 2: preview

Every target site is listed as a card with each setting that would change, its current value ("Now") and the new one ("After"). Three states:

• N settings change: this site will be saved when you confirm.
• No change: this site already has these values. It is greyed out and will not be saved, purged or written to, and nothing appears on its Activity page.
• Refused: the site could not be read (for example it no longer exists). It is left out; the others are unaffected.

A site that is not switched on yet (no licence validated there) is marked with a lock: the values are saved and take effect the moment a licence switches it on; nothing is written to the server before then.

Back returns to step 1 with nothing written. Cancel returns to the Sites tab with nothing written.

Step 3: apply

Clicking Apply to N sites writes exactly the values shown in the preview, even if someone edits the source site in the meantime. For each site that was marked as changing, and only those, the plugin:

1. saves the chosen section on that site through the same checks as a save on the site itself (the same sanitizer, so an out-of-range value is clamped the same way);
2. rewrites that site's settings snapshot for the cache drop-in (runtime-config-<id>.php);
3. rewrites the shared .htaccess Browser Caching rules if the site is switched on and the section touches them;
4. purges that site's cached pages if a setting that shapes page output changed (no other site is purged);
5. records one row per changed setting on that site's Activity page, with source network.<user id> (the network administrator's user id) and the value before and after.

The Sites tab then shows a notice: how many sites changed, how many already matched (left untouched) and how many were refused.

Undoing an apply

• One site: open that site's Activity page (the Activity button on the Sites tab), find the rows with source network.<id>, click Revert on each. Each revert restores the "Now" value the preview showed for that one setting, and is itself recorded.
• Several sites at once: run Apply settings again from a source that still has the old values (a site you did not change, or the plugin defaults), tick the sites, preview, confirm.
• A site that was not switched on keeps the applied values until reverted; revert works there too.

An Unused CSS/JS rule that names a file a site never loads does nothing on that site: a rule only unloads what the site actually enqueues.

Asking the assistant

The AI Assistant on any site can answer questions about these screens from this article: where they are, what each step writes, what a "network" row on the Activity page means and how to revert it. It cannot run an apply or a purge for you; those stay behind the confirm buttons.

Activating on a network

Activate the plugin per site, or network-activate it. Network activation runs the activation steps on every site in turn, so each site starts with its own settings, its own runtime snapshot and its own Pro switch-on state; the free page cache is on for every site at once, while a site that has never had Caching Out Pro starts with Pro locked until a licence is validated on it (see Licensing); a site that already had Pro stays switched on. Each site's Filesystem Check shows that site's activation report.

The drop-in, WP_CACHE and the Browser Caching rules are written once for the whole install by whichever site activates first, because WordPress has one wp-content and one wp-config.php.

Licensing on a network

Today the licence server counts each site's address separately, so every subsite that validates a licence counts as one site against the licence's site limit. Enter the licence on each site you want switched on. A network-level licence entered once in Network Admin is planned.

Troubleshooting

Related

• Page Caching
• Licensing
• Activity (change record)