Definition:
A cache is a store that keeps copies of data or results so they can be reused without having to retrieve or calculate them again for every request. On a website, it can store images, stylesheets, responses or generated pages, reducing some of the work needed to display them.
It is not limited to the visitor’s device. A cache can exist in the browser, on the server hosting the application or in a CDN, which distributes copies from other servers. Each layer has its own rules and may hold a different version of the same resource.
Stored data does not necessarily remain current indefinitely. The system needs to determine when it can reuse the data, when it must check for changes and when it must discard or replace it.
Benefits of caching
Reusing resources can reduce data transfers, database queries and repeated page generation. This can decrease response times and server load, especially when many requests need the same information.
For example, a browser can reuse a stylesheet it has already downloaded when visiting another page on the site. A server can deliver a previously generated page without running all the processes that build it again. The benefit depends on a reusable copy being available; the first request may require the resource to be retrieved or generated.
A faster response can improve the user experience, but caching does not by itself fix excessively large images, inefficient code or design problems.
With HTTP caching, the server can communicate rules through headers such as Cache-Control. It can also provide validators, such as ETag, to check whether a copy is still valid without transferring its entire content again. The no-cache directive requires validation before reusing the response; no-store indicates that it must not be stored.
Configuration must account for updating copies and handling personalised content. A private response, a shopping cart or account details must not be delivered to another user through an incorrectly configured shared cache. When a page changes, related copies that still show outdated information may also need to be invalidated.
How to clear the cache
Clearing a cache removes the copies stored in the layer being targeted. In a browser, deleting cached files alone is not the same as deleting cookies, passwords or browsing history. These are different categories, although some clearing options allow them to be deleted together.
The location and names of the options can change depending on the version and device. In commonly used browsers, it is useful to distinguish these operations:
- Google Chrome: open the option for deleting browsing data, choose the time range and select cached images and files. Check the other boxes to avoid deleting cookies or other data unnecessarily.
- Safari: on a Mac, Settings > Privacy > Manage Website Data allows data from one or more sites to be removed. This is not an operation limited to cached files: it can also delete cookies and sign users out. On iPhone and iPad, the options are managed through the device’s Safari settings.
- Firefox: use the browsing-data clearing options and select the category for temporary files or cached web content. Check cookies, site data and history separately before confirming.
After the cache is emptied, the next load may be slower because resources must be retrieved again. There is no need to clear it routinely: it can be useful for diagnosing display problems or checking an update.
Clearing the browser cache does not empty the server or CDN cache. If a website continues to show an old version, the layer serving it must be identified. When the tool allows it, a specific URL can be purged instead of removing all cached copies of the site.
WordPress caching plugins
Caching plugins can reduce repeated page generation and make stored copies easier to manage. They are not always essential: some hosting services already provide page or object caching. Before adding another system, it is worth checking which features are active and how they work together.
The available tools include these six examples, with different features and requirements:
- WP Super Cache: generates static HTML files from WordPress pages so they can be served without running the entire dynamic process on every visit. It includes options for controlling the delivery and renewal of these copies.
- W3 Total Cache: allows different types of caching and CDN integrations to be configured. Some features depend on the services and resources available on the server; enabling every option does not guarantee a better result.
- WP Rocket: combines page caching, preloading and other optimisation features. Its clearing rules allow copies to be renewed when content changes, although exclusions and compatibility must be reviewed for each site.
- LiteSpeed Cache: combines optimisation features with server-cache integration. Its page caching requires compatible infrastructure, such as a LiteSpeed server or QUIC.cloud; installing the plugin on any hosting service does not enable that feature by itself.
- Cache Enabler: creates static HTML files and stores them on the server. It allows their expiry and clearing to be managed, avoiding the need to generate each page from scratch for every request.
- Comet Cache: stores generated versions of pages and provides exclusion and clearing rules. Handling of logged-in users and other special cases depends on the configuration and edition used.
These tools should not be treated as a ranking of the best options. The choice depends on the hosting environment, plugin maintenance, required features and tests on the actual website. Layering several page-caching systems without coordination can make updates and troubleshooting more difficult.
After configuration, both speed and the operation of forms, sessions, shopping carts and private areas should be checked. A page delivered faster but displaying incorrect data is not an improvement to the site.