ELI5: how browser cookies work

What is a browser cookie?

A browser cookie is like a tiny sticky note that a website puts on your computer [2]. When you visit a website, the server sends this small piece of information to your browser, and your browser saves it [3].

Why do websites use cookies?

Websites use cookies to remember things about you, like your username or what items you put in your shopping cart [5]. When you come back to the website later, your browser sends that sticky note back to the server, so the website knows who you are [5].

What information do they store?

Cookies store identifying information that helps websites recognize you when you return [3]. This could be your login details, your preferences, or items you were looking at [4].

How does the cookie travel back and forth?

When you first visit a website, the server sends you a cookie through special instructions called HTTP headers [1]. Later, when you visit that same website again, your browser automatically sends the cookie information back to the server [5].