The Libraries tab manages the libraries in your space. In a read-only space it only shows what’s there: installing, updating, removing and checking for updates are hidden, with a note saying why (a read-only server doesn’t reach other servers, so there is nothing to check against). It reloads every time you show the tab, so what you see matches your space.

${widgets.commandButton("Workbench: Libraries")} opens this tab in the Workbench.

The toolbar has:

Filter libraries: narrows installed libraries by name and available ones by name, description and page.
Install…: asks for a library or plug URI (https://… or github:…) and installs it. For a plug (a URI ending in .plug.js) it also asks where to save it.
Add repository…: asks for a Repository URI and the page to put it on (always under Library/Repository/), then adds it so its libraries show up under Available.
Check for updates: compares each installed library and repository with its source, and shows the result beside it (see below).
Update all: updates every installed library that can be updated, with progress. It only shows when there is something to update.

Below it are three sections, each with its own error and info banner:

Installed: the libraries you installed, plus plugs that no library brought along. Built-in libraries (on Library/Std/ pages, or without a share URI) are marked built-in and can’t be updated or removed. Libraries in dev mode are marked dev mode and are left alone, too. Click a row to open its page.
Available: the libraries your repositories offer, grouped by repository, with the recommended Std repository first. Install puts one in your space. Available library titles open their configured website. When no website is configured, the title opens the library’s source page using the browser URL for its URI (for example, expanding a github: URI to its GitHub file page).
Repositories: the repositories you added, with Update all to refresh all of them. Any that fail are listed with the reason. The built-in repositories (Std and SilverBulletMD) update like the others but can’t be removed.

A library that requires other libraries lists them by name, each marked installed or not installed, both on its Available card (installing it installs those too) and on its Installed row. An installed library that others require says Required by and which. A requires entry that can’t be used, such as a path starting with /, shows why, and installing that library fails until it is fixed.

An installed library or repository row shows its share URI. Its context menu offers:

Update: pulls the latest version from its source. When you edited a library here and its source changed too, it asks before replacing your edits.
Revert: in place of Update when a check found a library changed locally (edited here, unchanged at its source): discards your edits and restores the installed version, after asking.
Open page: opens its page, the same as clicking the row.
Copy URI: copies its share URI.
Remove: removes it, after asking. A library that another installed library requires can’t be removed: Remove is grayed out, and its tooltip says which to remove first.

Plugs only offer Remove.

Checking for updates

Check for updates reads the source of every library you installed (not built-in or dev-mode ones) and every repository you added.