What Are Cookies?
Cookies are small pieces of text data that websites store in your browser. Invented in 1994 by an engineer at Netscape, they have since become a foundational web technology.
The original purpose of cookies is to give "memory" to the stateless HTTP protocol. They play a vital role in maintaining login sessions, preserving shopping carts, remembering language preferences, and supporting many other conveniences on the web.
First-Party Cookies vs. Third-Party Cookies
First-Party Cookies
These are cookies set by the website you are currently visiting. They are used for maintaining login state, saving user preferences, and managing shopping carts. Generally useful, blocking them can cause websites to malfunction.
Third-Party Cookies
These are cookies set by a domain other than the one you are visiting. They are primarily used by advertising networks and analytics services to track user behavior across multiple websites. From a privacy standpoint, third-party cookies are the most controversial.
How Ad Tracking Works
Ad tracking typically follows this process:
- You visit Website A, and a script from an embedded ad network sets a third-party cookie
- You then visit Website B, and the same ad network's script reads that cookie
- The ad network now knows you visited both Site A and Site B
- Over time, this accumulated data builds a user profile based on your interests
- Personalized ads are served based on that profile
This process runs simultaneously across hundreds of ad networks without the user's awareness.
Tracking Technologies Beyond Cookies
Even if you block cookies, other technologies can still track you.
Browser Fingerprinting
A technique that identifies users by combining browser and device configuration data. Unlike cookies, it stores no data on the device, making it difficult to delete or block. For more details, see our browser fingerprinting guide.
Local Storage and IndexedDB
These technologies can store larger amounts of data in the browser than cookies. Even after deleting cookies, tracking IDs may persist in these storage mechanisms.
ETag and Cache Tracking
This method exploits the HTTP caching mechanism to identify users. The server returns a unique ETag, which is read back on the next visit to track the user.
Pixel Tracking
A 1×1 transparent pixel image is embedded in a web page or email. The loading request for this image is used to track user behavior.
How to Manage Cookies
Block Third-Party Cookies in Browser Settings
All major browsers offer settings to block third-party cookies. Safari, Firefox, and Brave block them by default. Chrome is also phasing out third-party cookies.
Set Cookies to Auto-Delete
Configuring your browser to automatically delete cookies when closed prevents long-term tracking. However, this comes with the trade-off of needing to log in again each time.
Use Privacy Extensions
- uBlock Origin: Comprehensively blocks ads and trackers
- Privacy Badger: Automatically learns and blocks trackers
- Cookie AutoDelete: Automatically deletes cookies when a tab is closed
Use Private Browsing Mode
In private browsing (incognito) mode, cookies are automatically deleted when the browser is closed. However, it does not encrypt your traffic or hide your IP address, so it does not provide complete anonymity.
Check Your Cookie Status with Kakunin-san
The Kakunin-san homepage displays your current cookie information and security score. A high cookie count is reflected in the security score, so make it a habit to check and clean up regularly.