Cookies are small text files that a website saves on your phone, tablet or computer when you visit it. Your browser stores them and then sends them back to the same website when you move around the site or come back later. They help websites remember things like your settings, what is in your cart, or that you have already seen the cookie banner.

HTTP by itself is “stateless”, which means each page load does not remember what happened on the previous one. Cookies fix this by giving the website a tiny bit of memory between requests. For example, a cookie can remember that you are logged in or which language you picked.

There are different types of cookies. “Session” cookies only last until you close your browser; then they are deleted. “Persistent” cookies stay for a longer time (for example a few days or months) so the website can remember your choices between visits. Websites choose an expiry time and the browser automatically deletes the cookie after that date.

You can also split cookies into “first‑party” and “third‑party”. First‑party cookies are set by the website you are actually visiting (its own domain) and are mostly used for basic site features and preferences. Third‑party cookies are set by other domains that are loaded into the page, such as advertising networks, analytics providers or social media widgets. These third‑party cookies are often used to follow your activity across multiple websites and build a profile for advertising.

Cookies can be grouped by what they are used for. “Strictly necessary” or “essential” cookies are needed for the site to work at all, for example keeping you logged in, moving through checkout, or remembering your cookie choice. “Preference” or “functional” cookies remember things like language, layout or saved items to make the site feel more personalised. “Analytics” or “performance” cookies help the site owner understand which pages are popular, how long visitors stay, and where problems might be, usually in an aggregated way. “Marketing” or “tracking” cookies are used to follow your browsing and show you targeted ads.

Technically, a cookie is created when the server sends a response with a Set‑Cookie header that contains the cookie’s name, value and some attributes (like expiry date, domain and security flags). The browser stores this information, then automatically adds it to future requests to that site in a Cookie header. Cookies can also be created by JavaScript in the page, unless they have been marked “HttpOnly”, which blocks access from scripts for security.

Cookies have several important security‑related attributes. The “Secure” flag means the browser will only send the cookie over HTTPS, not plain HTTP. The “SameSite” attribute controls whether the cookie is sent with cross‑site requests, which helps reduce some tracking and CSRF attacks. The domain and path settings limit which parts of a site and which subdomains can see the cookie.

Because cookies can be used to track people and sometimes hold personal data, privacy laws in the EU (including Ireland) and under GDPR require websites to get valid consent for most non‑essential cookies. Consent must be freely given, specific, informed and unambiguous, and it must be just as easy to withdraw it as to give it. Guidance from the Irish Data Protection Commission also says you should not rely on “implied” consent from scrolling, should avoid pre‑ticked boxes, should clearly explain cookie purposes, and should normally refresh cookie consent at least every six months.

As a user, you stay in control of cookies. Every modern browser lets you see stored cookies, delete them, block new ones, or clear cookies when you close the browser. You can usually choose to block third‑party cookies, which cuts down cross‑site tracking while still allowing most sites to function. If you block or delete certain cookies, some features like staying logged in, saving preferences, or personalised recommendations may stop working properly.

In summary, cookies are a basic building block of how the web works: they give websites memory so they can keep you logged in, remember your settings and make things smoother. At the same time, some cookies are used for detailed tracking and advertising, which is why there are cookie banners, choices and strict rules about consent and transparency.
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