Browsers and cookies: what they are and what to accept

What a browser does

A browser is the app you use to visit websites. Common ones include Google Chrome, Apple Safari, Microsoft Edge and Mozilla Firefox. On a phone, it may be the app with a compass or globe icon.

When you type a web address, the browser asks the right server for that page, receives a bundle of text, pictures and instructions, and then assembles it on your screen. It is a bit like a chef who receives a recipe and ingredients and turns them into a finished meal. For the full journey, see What happens when you open a website.

Your browser also keeps track of things for you: your history, saved passwords, bookmarks, downloaded files and cookies.

So what is a cookie?

A cookie is a tiny text file that a website asks your browser to keep. Next time you visit, the browser hands it back, so the site can recognise you.

Think of a cloakroom ticket. When you hand over your coat, you get a numbered ticket. Later, you show the ticket and get the right coat back. The cookie is the ticket. It does not usually contain your details directly, just a reference the website can look up.

Cookies are not programs and cannot install anything on your device. They are just notes.

Helpful cookies and tracking cookies

Cookies are used for very different purposes:

• Essential: keep you signed in, remember what is in your shopping basket, and keep secure pages working.
• Preferences: remember your language, region or text size.
• Analytics: help the site count visitors and see which pages are popular.
• Advertising and tracking: build a picture of your interests so you can be shown targeted adverts, sometimes across many different websites.

A first-party cookie comes from the site you are actually on. A third-party cookie comes from another company whose content is embedded in the page, such as an advertising network. Because the same advertising company appears on many sites, its cookie can link your visits together. That is how an advert for shoes you looked at can follow you around the web. Several browsers now block or limit third-party cookies by default, but other tracking methods exist too.

Those cookie banners

In the UK and EU, sites must ask your permission before setting non-essential cookies. That is why you see a banner on almost every site. You do not have to accept everything.

1. Look for Reject all or Necessary only. Choosing it still lets the site work properly.
2. If there is only Accept and Manage, choose Manage and switch off advertising and tracking options.
3. If you change your mind later, many sites have a "cookie settings" link at the bottom of the page.

Tip: Rejecting tracking cookies does not stop adverts. You will still see them; they just will not be based on your browsing elsewhere.

Keeping your browser safe and tidy

• Keep it updated. Browser updates fix security holes. Most update themselves, but restart the browser now and then so updates can finish.
• Check the address bar. Before typing a password, make sure the web address is the real one. Scam sites often use names that look almost right. See Phishing basics.
• Be careful with extensions. Add-ons can see what you do on websites. Only install ones you really need, from the official store, and remove ones you no longer use.
• Use private browsing where it fits. A private or incognito window forgets cookies and history when you close it. It is handy on a shared computer, but it does not hide you from websites, your employer or your internet provider.
• Clear cookies if a site misbehaves. Clearing cookies for one site often fixes odd log-in problems. Clearing all cookies will sign you out of everything, so have your passwords ready.

Common mistakes

Thinking cookies are viruses: they are not. Thinking private mode makes you invisible: it does not. Clicking "Accept all" out of habit: it is worth the extra second to choose "Reject all". And saving passwords in a browser on a shared family computer without a separate user account for each person.

Want the technical version? See Application protocols.