Definition
Caching is storing copies of files or whole pages so later requests can be served quickly, without rebuilding or re-downloading them.
Caching explained
Websites use several layers of caching:
- Browser caching: the visitor's browser keeps images, CSS and scripts, so repeat visits load faster. It is controlled with HTTP Cache-Control headers.
- Page caching: the server or a plugin stores the finished HTML of a page, so it doesn't need to run code and database queries for every visitor.
- CDN caching: copies of files, or whole pages, are stored at servers near visitors.
- Object caching: results of expensive database queries are kept in memory.
Good caching dramatically reduces server response time and load. The main risk is serving outdated content: a price change, a fixed typo or an updated redirect that some visitors or crawlers don't see because an old copy is cached. Use versioned file names for assets, set sensible cache lifetimes, and clear the relevant caches when content changes.
Pages that must be personal, such as carts and account areas, should not be cached for everyone.
Example
Your WordPress site rebuilds every page from the database on each visit, so it slows down whenever a campaign sends traffic. Enabling page caching and long browser cache lifetimes for images and scripts keeps pages fast during the next campaign.
Why it matters
Caching is the cheapest way to make a site fast for most visitors, and to keep it fast under traffic spikes.
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Related terms
- TTFB (Time to First Byte)TTFB (Time to First Byte) is the time from requesting a page to receiving the first byte of the response; web.dev suggests 0.8 seconds or less.
- CDN (Content Delivery Network)A CDN (content delivery network) is a network of servers in many locations that delivers your site's files from the one nearest each visitor.
- LCP (Largest Contentful Paint)LCP (Largest Contentful Paint) measures how long the largest image, video or text block in view takes to render; 2.5 seconds or less is good.
- WordPress pluginA WordPress plugin is an add-on that extends what a WordPress site can do, such as forms, SEO settings, caching, security or e-commerce.