Cookies are small files that websites store on your device to remember information about you
A cookie is a tiny text file — usually just a few kilobytes — that a website saves to your computer or phone. When you visit that website again, your browser sends the cookie back to it. This lets the site remember things about you without asking you to log in every single time or re-enter the same information over and over.
Cookies are not programs and cannot damage your device. They cannot see your files, steal your passwords, or run code on your computer. They are just data — usually a string of letters and numbers that means something only to the website that created it.
Most of the internet runs on cookies. Without them, you would have to log into your email account every time you refreshed the page, shopping sites would forget what you put in your cart, and websites would have no way to remember your preferences.
Key Takeaways
- Cookies are small text files that websites store on your device to remember information about your visits and preferences.
- First-party cookies come from the website you are visiting; third-party cookies come from advertisers or analytics companies and track you across multiple sites.
- You can see what cookies are stored on your device and delete them through your browser settings, though deleting them may log you out of websites.
- Cookies cannot run programs, steal passwords, or access your files — they are just text data that websites read back to themselves.
- Most websites use cookies to keep you logged in, remember your cart, and track which pages you visit so they can show you relevant ads.
How cookies actually work when you visit a website
When you land on a website, the server sends your browser a small instruction that says "store this cookie." Your browser saves it as a text file in a folder on your device. The next time you visit that same website, your browser automatically reads that file and sends it back to the server before the page even loads.
The website then uses that cookie to look up information about you. If you logged in before, the cookie might contain a session ID — a code that tells the server "this is Marcus, and he is already logged in." If you added items to a shopping cart, the cookie might hold a list of product IDs. If you set a dark mode preference, the cookie remembers that too.
This happens in the background without you seeing it. You do not have to do anything. The browser handles the whole exchange automatically.
First-party cookies versus third-party cookies
First-party cookies come directly from the website you are visiting. When you log into Gmail, Google sets a first-party cookie on your device. When you add something to your Amazon cart, Amazon sets a first-party cookie. These cookies only get sent back to the website that created them, so Amazon cannot read Google's cookies and vice versa.
Third-party cookies come from a different company than the one running the website you are on. An advertising network like Google Ads or Facebook Pixel might set a cookie on your device when you visit a news site. That cookie tracks you across many different websites — the news site, a clothing store, a recipe blog — and reports back to the ad company about where you have been. This is how advertisers build a profile of your interests and show you targeted ads.
Third-party cookies are the reason you see ads for something you looked at on one website appearing on a completely different website hours later. Most browsers now block third-party cookies by default, though some still allow them.
What information do cookies actually store
Cookies store whatever the website decides to put in them. Common examples include your login session ID, your username, your language preference, items in your shopping cart, the date you last visited, and your timezone. Some cookies store a unique ID that an ad company uses to track you across sites.
Cookies cannot store your password directly — that would be a serious security flaw. They also cannot see your files, your email, your browsing history on other sites, or anything else on your device. They can only store what the website explicitly puts into them, and they can only be read by the website that created them (with the exception of third-party cookies, which are read by the ad or analytics company).
You can see exactly what cookies are stored on your device by opening your browser settings. In Chrome, go to Settings > Privacy and Security > Cookies and Other Site Data. In Firefox, go to Settings > Privacy & Security > Cookies and Site Data. You will see a list of every website that has stored a cookie on your device and can delete any or all of them.
Why websites use cookies and what happens if you delete them
Websites use cookies for three main reasons: to keep you logged in, to remember your preferences, and to track your behavior for advertising or analytics. Without cookies, every time you refreshed a page you would be logged out. Every time you visited a site, it would not remember whether you prefer dark mode or light mode, English or Spanish, or what items you had in your cart.
If you delete all your cookies, you will be logged out of every website. The next time you visit a site, it will not remember you. Shopping carts will be empty. Saved preferences will be gone. For most people, this is not a problem — you can log back in, and the site will set new cookies. But if you delete cookies regularly, you will find yourself logging in more often.
Some people delete cookies regularly for privacy reasons. Deleting third-party cookies in particular reduces the amount of tracking that ad companies can do across sites. Most modern browsers let you block third-party cookies entirely without deleting first-party cookies, which is a middle ground — you stay logged in and keep your preferences, but advertisers cannot track you as easily.
Cookie consent notices and what they actually mean
Many websites now show a banner when you first visit asking for permission to set cookies. These notices exist because of privacy laws in Europe (GDPR) and California (CCPA) that require websites to get your consent before storing certain types of cookies, especially tracking cookies used for advertising.
When you click "Accept All," you are giving the website permission to set both first-party cookies (which it needs to function) and third-party cookies (which are used for tracking and ads). When you click "Reject" or "Manage Preferences," you can usually block third-party cookies while still allowing first-party ones. Some sites will not let you reject all cookies — they will only let you manage which types you accept.
These notices do not mean cookies are dangerous. They are just a legal requirement to tell you what is happening and give you some control over it.
How to manage cookies in your browser
Every major browser lets you control cookies through settings. In Chrome, go to Settings > Privacy and Security > Cookies and Other Site Data. You can choose to block all cookies, block third-party cookies only, or allow all cookies. You can also see a list of every site that has stored a cookie and delete cookies from specific sites.
In Firefox, go to Settings > Privacy & Security > Cookies and Site Data. You have similar options: allow all cookies, block third-party cookies, or block all cookies. Firefox also lets you delete cookies automatically when you close the browser.
In Safari on Mac or iPhone, go to Settings > Privacy and look for "Cookies and Website Data." You can block all cookies, block third-party cookies, or allow all. Safari also has an option to delete cookies automatically.
In Edge, go to Settings > Privacy, Search, and Services > Clear Browsing Data. You can choose what to delete and how often — every time you close the browser, weekly, or manually.
Frequently Asked Questions
Can cookies give me a virus or malware?
No. Cookies are text files only — they cannot run programs or execute code. They cannot install software, download files, or damage your device. A virus or malware would have to come from somewhere else, like a malicious email attachment or a compromised website.
Can a website read cookies that another website set?
No, with one exception. First-party cookies are locked to the website that created them — Amazon cannot read Google's cookies. Third-party cookies, however, are set by ad or analytics companies and can be read across many different websites, which is how tracking works. Most browsers now block third-party cookies by default.
What is the difference between cookies and tracking pixels?
A tracking pixel is a tiny invisible image that a website embeds in a page. When you load the page, your browser downloads the image and the server records that you visited. Pixels do not store data on your device the way cookies do — they just report back to the company that owns them. Many websites use both cookies and pixels together for tracking.
If I clear my cookies, will websites know I deleted them?
No. When you delete a cookie, it is simply gone from your device. The website has no way to know you deleted it. The next time you visit, the website will just see that no cookie is present and will treat you as a new visitor, setting a new cookie if it wants to.
Do I need to delete cookies regularly for security?
Not for security — cookies themselves cannot harm you. You might delete cookies for privacy reasons if you want to reduce tracking by advertisers, or if you share a device with other people and want to log out of your accounts. Most people do not need to delete cookies regularly.