Cookies – Definition and meaning
What is Cookies? Cookies: How they work, where they are used, advantages, risks and concrete examples for everyday use in web development.
Definition and purpose of cookies
Cookies are small text files that are stored by a website in a user's browser. They store information that is required during the visit or during subsequent interactions with the website. This allows website operators to identify individual users, manage ongoing sessions or save personal settings. Cookies also allow user behaviour to be tracked and web applications to be customised. For modern web applications, they are a fundamental tool that significantly supports user-friendliness and personalisation.
Functionality and technical background
From a technical perspective, cookies are structured key-value pairs that are stored in the browser. In addition to a name and a value, they often contain other attributes such as expiry date, path or domain assignment. Each time a website is visited later, the browser automatically transfers the relevant cookies to the server - a function that is used in session management, for example. In an online shop, the content of the shopping basket is retained even if the user navigates between different product pages or logs in again.
Cookies are also used to manage language settings: If a visitor selects French on an international website, a cookie saves this information. Future visits are then presented directly in the selected language. Developers can set and manage cookies both on the server side (e.g. using setcookie() in PHP) and on the client side using JavaScript. Session cookies, which are removed when the browser is closed, and persistent cookies, which last for a longer period of time depending on a predefined expiry date, are designed differently.
Purposes and practical examples
The use of cookies in everyday web use is wide-ranging. They are often used to temporarily store login data so that there is no need to log in again each time you visit a website. In online retail, they save the individual items in the shopping basket even over a longer session break. Analysis and marketing tools, such as Google Analytics, use cookies to evaluate user behaviour on the website, which enables targeted optimisation. Cookies are also regularly used to store individual user preferences - such as the selection of a specific font size or colour design.
A tangible example is the cookie consent request on websites. On the first visit, a notice on data usage usually appears, asking for consent to store certain cookies - after the response, the decision itself is stored in a cookie. In this way, the notice does not appear again on subsequent visits. Careful handling is recommended in everyday development work: Cookies should be used selectively to avoid unnecessary data storage and performance losses and to comply with applicable data protection regulations.
Advantages, challenges and recommendations
Cookies offer numerous advantages for developers and operators. They can be used to create personalised online experiences and efficient web applications without the need for complex storage solutions. The technical standard and broad browser support facilitate integration in everyday life. At the same time, they pose growing challenges when it comes to implementing data protection regulations such as the GDPR and ePrivacy Directive. Website visitors today expect clear instructions on the use of cookies and want to decide for themselves what information is stored. Many browsers now significantly restrict the use of tracking and third-party cookies to ensure user privacy.
A tried and tested approach is to limit the use of cookies to what is absolutely necessary, to make them as short-lived as possible and to document their purpose in a comprehensible manner. For security-relevant applications, the use of secure and HTTP-only flags is recommended to restrict access to sensitive data. Complex interactions can be realised efficiently by combining cookies and supplementary web storage methods such as localStorage or sessionStorage.
Frequently asked questions
Cookies are small text files that are stored by websites in a user's browser. They are used to store information that is important for interaction with the website. This includes, for example, login data, language settings or the contents of the shopping basket in an online shop. Cookies enable a personalised user experience as they analyse and store the user's behaviour and preferences.
Cookies work as structured key-value pairs that are stored in the browser. Each time a website is visited, the browser automatically transmits the relevant cookies to the server. This function is often used to manage sessions or store user preferences. Cookies can be set on both the server and the client side and differ in terms of their lifespan, with session cookies being deleted when the browser is closed and persistent cookies lasting for a longer period of time.
Cookies are essential in online retail to ensure a smooth user experience. For example, they save the items in the shopping basket so that users can continue to access their selection even after interrupting their visit. In addition, cookies make it possible to save login data, which eliminates the need to log in again. They also contribute to the analysis of user behaviour, which is used to optimise offers and personalise marketing measures.
Session cookies are temporary cookies that only exist during a browser session and are deleted when the browser is closed. They are often used to store information during a visit to a website. In contrast, persistent cookies are created for the long term and remain stored in the browser until they expire or are deleted manually. These cookies are useful for storing user preferences across multiple visits.
Cookies offer website operators numerous advantages by enabling a personalised user experience and optimising interaction with the website. They facilitate session management, save login data and enable user behaviour to be analysed. This allows operators to make targeted adjustments and improve user-friendliness. Cookies are also easy to implement and support the efficiency of web applications.
Data protection laws such as the GDPR and the ePrivacy Directive have a significant impact on the use of cookies. Website operators are obliged to provide clear information about the use of cookies and to obtain user consent. This applies in particular to tracking cookies and third-party cookies, which are often used to analyse user behaviour. Operators must ensure that they respect the privacy of users and handle the collected data transparently.
Users can customise their cookie settings in most web browsers. This is usually done via the browser's settings or privacy options, where they can decide whether cookies should be accepted, blocked or deleted. Many browsers also offer the option of managing specific cookies from certain websites. In addition, users can use browser plugins to further protect their privacy and control the use of cookies.
Third-party cookies are cookies that are set by a domain that is not the one the user is currently visiting. These cookies are often used by advertising networks and analytics providers to track user behaviour across different websites. They enable personalised advertising and the analysis of user interactions. However, due to privacy concerns, many browsers have started to restrict the use of third-party cookies to protect user privacy.