What Is a Cookie Used For? Website Cookies Explained
Learn what a cookie is used for on websites, from session management to advertising. Understand the types, privacy laws, and how to manage them.
What is a cookie used for on the websites you visit every day? In simple terms, a cookie is a small text file that a website places on your browser to remember information about you between page visits and sessions. Cookies power everything from keeping you logged in to tracking your browsing behaviour across the internet.
This article explains how website cookies work, the different types, what privacy laws say about them, and how you can control them. This is educational content and does not constitute legal advice. Consult a qualified attorney for guidance on your specific compliance obligations.
What Is a Cookie and How Does It Work?
A cookie is a small piece of data, typically no larger than four kilobytes, that a web server sends to your browser. Your browser stores the cookie and sends it back to the server with every subsequent request to that website. This simple mechanism gives websites a form of memory that HTTP, the protocol powering the web, does not natively provide.
When you visit a website for the first time, the server can include a Set-Cookie header in its response. Your browser saves this cookie and automatically attaches it to future requests to that same domain. The cookie might contain a session identifier, a preference setting, or a tracking token.
Without cookies, every page load would be a completely fresh interaction. The website would not know whether you are logged in, what items are in your shopping cart, or which language you prefer. Cookies solve this by maintaining state between otherwise stateless HTTP requests.
The Main Purposes of Website Cookies
Understanding what cookies are used for requires looking at the distinct categories of cookie usage. Each serves a different function, and privacy regulations treat them differently.
Session Management
Session cookies are the most fundamental type. When you log in to a website, the server creates a session and sends your browser a cookie containing a unique session identifier. On every subsequent page you visit, your browser sends that identifier back, allowing the server to recognise you without requiring you to log in again.
Session management cookies also handle:
- Shopping cart contents on ecommerce sites
- Multi-step form progress (keeping data as you move between pages)
- Security tokens that protect against cross-site request forgery (CSRF) attacks
- Load balancer routing to maintain connection to the same server
These cookies are generally considered essential for website functionality and are exempt from consent requirements under most privacy regulations.
Personalisation and Preferences
Preference cookies remember your choices so the website can tailor your experience. Common examples include:
- Language selection: The site displays content in your preferred language without asking each time
- Theme settings: Light mode, dark mode, or font size preferences persist across visits
- Regional settings: Currency, measurement units, or local content based on your selected region
- Interface customisation: Dashboard layouts, collapsed menus, or dismissed notifications
These cookies improve usability but are not strictly necessary for the website to function. Under the GDPR and ePrivacy Directive, websites typically need consent to set preference cookies, though some regulators classify certain preference cookies as essential depending on the context.
Analytics and Performance
Analytics cookies track how visitors use a website. Services like Google Analytics, Matomo, and similar platforms use cookies to collect data including:
- Which pages you visit and in what order
- How long you spend on each page
- Where you came from (search engine, social media, direct link)
- What device, browser, and operating system you use
- Scroll depth and interaction patterns
This data helps website operators understand what content resonates, where users encounter problems, and how to improve the site. Analytics cookies are not essential for website functionality, and the GDPR requires consent before setting them. The French data protection authority (CNIL) and other European regulators have issued specific guidance on analytics cookies, with some exemptions for privacy-respecting tools configured to not track users across sites.
Advertising and Tracking
Advertising cookies are what most people think of when they hear about cookie privacy concerns. These cookies, predominantly third-party cookies, track your browsing activity across multiple websites to build a profile of your interests and serve targeted advertisements.
Here is how advertising cookies typically work:
- An advertising network places its code (a tracking pixel or script) on thousands of websites
- When you visit any of those websites, the ad network sets a cookie in your browser
- As you browse from site to site, the ad network reads its cookie and records your path
- The network builds a profile of your interests based on the content of sites you visit
- Advertisers bid to show you ads based on your profile through real-time auction systems
This cross-site tracking capability is why third-party cookies have become the primary target of privacy regulations and browser restrictions. Google Chrome began phasing out third-party cookie support, following the approach already taken by Safari and Firefox, which block third-party cookies by default.
Functional and Security Cookies
Some cookies serve technical functions that fall between essential and optional:
- Fraud detection: Cookies that help identify suspicious login attempts or bot activity
- Content delivery network (CDN) routing: Cookies that direct your requests to the nearest server
- A/B testing: Cookies that ensure you see a consistent version of a page during a test
- Accessibility settings: Cookies remembering screen reader preferences or motion reduction choices
First-Party vs. Third-Party Cookies
The distinction between first-party and third-party cookies is central to understanding what cookies are used for and why they are regulated differently.
First-party cookies are set by the domain you are visiting. If you are on example.com, any cookie set by example.com is a first-party cookie. These typically handle session management, preferences, and first-party analytics.
Third-party cookies are set by a different domain than the one you are visiting. If example.com loads an advertising script from adnetwork.com, and that script sets a cookie, the adnetwork.com cookie is a third-party cookie. These enable cross-site tracking because adnetwork.com can read its cookie on every website that includes its script.
The privacy implications differ significantly:
- First-party cookies generally stay within a single website's context and serve the user's direct relationship with that site
- Third-party cookies can follow users across the entire web, building detailed browsing profiles without the user visiting the tracking company's website directly
Major browsers have responded to these concerns. Safari's Intelligent Tracking Prevention and Firefox's Enhanced Tracking Protection block most third-party cookies by default. Chrome has been moving toward restricting third-party cookies as well, with the Privacy Sandbox initiative offering alternative APIs for advertising use cases.
Privacy Laws That Regulate Cookie Usage
Several major privacy regulations govern how websites can use cookies. If you operate a website, understanding these laws determines what consent you need and how to obtain it.
EU ePrivacy Directive and GDPR
The ePrivacy Directive (2002/58/EC, amended by 2009/136/EC) is the primary EU law governing cookies. It requires websites to:
- Provide clear, comprehensive information about what each cookie does
- Obtain informed consent before setting non-essential cookies
- Allow users to refuse non-essential cookies without losing access to the service
The GDPR (Regulation 2016/679) supplements the ePrivacy Directive by defining the rules for valid consent. Under Article 7 of the GDPR, consent must be freely given, specific, informed, and unambiguous. Pre-ticked checkboxes do not constitute valid consent, as confirmed by the Court of Justice of the European Union in the Planet49 case (C-673/17).
Penalties for non-compliance are substantial. GDPR violations can result in fines up to 20 million EUR or four percent of global annual turnover, whichever is higher. Data protection authorities across Europe have issued significant fines specifically for cookie consent violations.
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Generate NowUK GDPR and PECR
The UK's Privacy and Electronic Communications Regulations (PECR) mirror the ePrivacy Directive's cookie consent requirements. Following Brexit, the UK GDPR operates alongside PECR to regulate cookie usage for UK users. The Information Commissioner's Office (ICO) has issued detailed guidance on cookies and actively enforces these requirements.
CCPA and CPRA (California)
The California Consumer Privacy Act and its amendment, the California Privacy Rights Act, take a different approach. Rather than requiring opt-in consent for cookies, these laws give California residents the right to:
- Know what personal information is collected about them
- Opt out of the sale or sharing of their personal information
- Request deletion of their personal information
Websites that use cookies to share data with advertising networks for cross-context behavioural advertising must provide a "Do Not Sell or Share My Personal Information" link. CCPA violations can result in penalties of $2,500 per unintentional violation and $7,500 per intentional violation.
Other Regulations
Privacy laws in Brazil (LGPD), Canada (PIPEDA), South Africa (POPIA), and numerous other jurisdictions also regulate cookie usage to varying degrees. If your website serves users internationally, you need to account for the strictest applicable regulation.
How Cookie Consent Works
Cookie consent management is how websites comply with laws requiring user permission before setting non-essential cookies. A cookie consent banner, also called a cookie consent management platform (CMP), presents users with information about the site's cookies and collects their consent choices.
An effective cookie consent system must:
- Block non-essential cookies until consent is given: Simply showing a banner while cookies fire in the background does not satisfy the GDPR's consent requirements
- Provide granular choices: Users should be able to accept or reject cookies by category (analytics, advertising, preferences) rather than facing an all-or-nothing choice
- Make refusal as easy as acceptance: The option to reject cookies should be as prominent and accessible as the option to accept. European regulators have specifically targeted "dark patterns" where the reject option requires extra clicks
- Record consent as proof: Maintain a log of when each user consented and to what categories, as evidence of compliance
- Allow consent withdrawal: Users must be able to change their cookie preferences at any time
If you operate a website, a cookie policy generator can help you create the disclosure document that explains what cookies your site uses and why. This policy works alongside your consent banner to satisfy transparency requirements. TermsBox provides both a cookie consent banner and automated cookie scanning that detects what cookies your site actually sets, keeping your policy accurate as your site evolves.
How to Control Cookies as a User
You have several options for managing cookies in your browser.
Browser Settings
Every major browser lets you control cookie behaviour:
- Block all third-party cookies: This stops cross-site tracking while preserving first-party functionality. Safari and Firefox do this by default.
- Clear cookies on exit: Your browser deletes all cookies when you close it, effectively resetting your tracking profile each session.
- Block all cookies: This breaks many websites but eliminates cookie tracking entirely.
- Manage site-specific permissions: Allow cookies from sites you trust while blocking them elsewhere.
Browser Extensions
Privacy-focused browser extensions provide more granular control:
- Ad blockers that prevent tracking scripts from loading in the first place
- Cookie managers that automatically delete cookies from sites you have not whitelisted
- Script blockers that prevent JavaScript-based cookie setting entirely
Do Not Track and Global Privacy Control
The Do Not Track (DNT) HTTP header was an early attempt at browser-based privacy signalling, but most websites ignore it because it was never backed by legal requirements. Global Privacy Control (GPC) is a newer standard that carries legal weight under the CCPA/CPRA. Websites that receive a GPC signal from a California resident must treat it as a valid opt-out of the sale or sharing of personal information.
What Cookies Are Used For in Ecommerce
Ecommerce websites rely heavily on cookies for core functionality and revenue optimisation. Understanding what cookies are used for in this context illustrates why cookie management requires careful thought.
Essential ecommerce cookies include:
- Shopping cart persistence (so items remain when you navigate between pages)
- Checkout session management
- Currency and shipping region selection
- Fraud prevention tokens
Marketing cookies in ecommerce serve purposes like:
- Retargeting ads that show you products you viewed but did not purchase
- Attribution tracking to determine which marketing channel drove a sale
- Personalised product recommendations based on browsing history
- Abandoned cart recovery campaigns
For ecommerce site operators, creating a compliant cookie policy and pairing it with a thorough privacy policy are practical first steps. These documents must accurately reflect the cookies your site uses, which can change as you add new features, payment providers, or marketing tools.
The Future of Cookies
The cookie landscape is shifting. Third-party cookies are being phased out across browsers, and the advertising industry is developing alternatives:
- Google's Privacy Sandbox: A set of APIs (Topics, Protected Audience, Attribution Reporting) designed to enable advertising use cases without individual cross-site tracking
- Server-side tracking: Moving analytics and tracking logic from the browser to the server, which avoids client-side cookie restrictions but raises its own privacy questions
- First-party data strategies: Businesses collecting data directly from their customers through logins, subscriptions, and direct interactions rather than relying on third-party tracking
- Contextual advertising: Serving ads based on the content of the page being viewed rather than the user's browsing history
These changes will reshape what cookies are used for, but the fundamental need for session management, personalisation, and analytics will remain. Privacy regulations will continue to evolve alongside the technology, making ongoing compliance monitoring essential for any website operator.
Frequently Asked Questions
What is a cookie used for on a website?
A website cookie is a small text file stored on your device that serves several purposes: keeping you logged in (session management), remembering your preferences like language or theme (personalisation), tracking which pages you visit (analytics), and delivering targeted advertisements based on your browsing behaviour. Cookies are essential for basic website functionality, but some types raise privacy concerns because they can track you across multiple websites.
Are cookies dangerous or harmful to my computer?
Cookies themselves are not dangerous. They are plain text files that cannot execute code, install software, or carry viruses. However, tracking cookies can collect detailed information about your browsing habits across multiple websites, which raises privacy concerns. The risk is not technical harm to your computer but rather the extent of personal data collection that third-party cookies enable, often without meaningful user awareness.
What is the difference between first-party and third-party cookies?
First-party cookies are set by the website you are visiting directly. They handle functions like keeping you logged in and remembering your shopping cart. Third-party cookies are set by external domains, typically advertising networks or analytics services, and can track your browsing activity across every website that loads their code. Privacy regulations focus primarily on third-party cookies because of their cross-site tracking capabilities.
Do websites legally need my consent to use cookies?
Under the EU ePrivacy Directive and GDPR, websites must obtain informed consent before setting non-essential cookies for users in the European Economic Area. The UK GDPR and PECR impose similar requirements. In the United States, the CCPA and CPRA give California residents the right to opt out of the sale or sharing of personal information collected through cookies. Essential cookies required for basic website functionality are generally exempt from consent requirements.