What are cookies used for?
A cookie is a small text file a website asks your browser to store, then reads back on later visits. That simple mechanism does everything from keeping you logged in to following you around the web for advertising. Here is what they are actually used for.
Keeping you logged in and remembering state
The original purpose of cookies — and still the most important — is memory. HTTP is "stateless": without help, a website forgets who you are between one click and the next. A cookie holds a small token (a session ID) so the server recognises you across pages, which is how staying logged in, keeping items in a shopping cart, and multi-step checkouts work at all.
These are "strictly necessary" cookies. They do not track you across other sites and the site genuinely cannot function without them, so under EU and UK rules they do not need consent.
Remembering your preferences
The next step up is convenience: remembering your language, currency, region, dark-mode choice, or that you already dismissed a notice. These "functional" cookies are not strictly necessary, so a site is supposed to ask before setting them.
Measuring how the site is used (analytics)
Site owners want to know which pages are popular, where people drop off, and how many unique visitors they get. Analytics cookies — like Google Analytics' _ga — assign each browser a random ID so visits can be counted and grouped into sessions.
Even though analytics feels harmless and the data is often "anonymised", these cookies still require consent in the EU and UK. First-party and anonymised does not exempt them.
Advertising and cross-site tracking
The most controversial use is marketing. Advertising cookies — like Meta's _fbp or Google's IDE — let ad networks recognise the same browser across many different websites, building a profile used to target ads and measure whether you bought something after seeing one.
This is the category cookie law was really written for, and it always needs clear, opt-in consent before the cookie is set.
Cookies like this
Scan any website and we'll list every cookie it sets — categorised, with the ones that load before consent flagged.
Related guides
General information to help you understand cookies — not legal advice.