Apps and Plugins
Adding something the shop does not do itself, what an app can reach, and removing one cleanly.
MarketPlace holds the things that extend your shop: apps, plugins and themes.
Apps and Plugins
An app is built against the platform's own interfaces and installed into your shop. It can add screens to the admin, extend the checkout and react to events.
A plugin is similar in effect and smaller in scope, usually adding one capability rather than a whole area.
Both are installed from the marketplace, and both can be removed.
Before Installing Anything
Three questions worth asking.
What does it need access to? An app is told what it may read and change when it is installed. An app that wants your customer list to change your shipping labels is asking for more than its job requires.
Who maintains it? A platform update can break something unmaintained, and the symptom will be in your shop rather than in theirs.
What happens if it goes away? Anything that holds data you cannot export is a decision you will find hard to reverse.
Install one at a time, on a quiet day
Two apps installed together make it impossible to tell which caused a problem. Install, use the shop normally for a day, then install the next.
What an App Can Reach
An app is granted specific permissions and cannot exceed them. It cannot see other shops on the platform, and it cannot read your payment credentials or your customers' cards, because neither of those is ever available to anything inside the shop.
Removing One
Uninstalling stops it running and removes its screens. Data it created may remain, and whether it is useful without the app varies.
If an app was adding something to your storefront, check your shop after removing it. A theme block or a script left behind by an app that is no longer there is the usual cause of a sudden layout problem following an uninstall.
Themes From the Marketplace
Themes are listed in the same place and behave differently: adding one to your library does not activate it, so you can look before switching. See Themes and Design.
When Something Breaks After Installing
Uninstall it first and check whether the problem goes. That is a two minute test that saves a long investigation, and it is also the question you will be asked.
If the problem persists after uninstalling, it was probably not the app, and the timing was coincidence. Both answers are useful.