Cookies are shared between tabs in Chrome because they are stored at the browser level, not at the tab level. When you open multiple tabs in Chrome, they all access the same cookie storage. This means if a website sets a cookie in one tab, that cookie will be available to the same website in another tab. This behavior applies to regular cookies, which are the standard mechanism for persisting user data like login sessions and preferences across browsing sessions.
However, there are exceptions. Private browsing tabs (Incognito mode) use separate cookie storage that doesn't interact with regular tabs. Additionally, if you're using Chrome's multi-profile feature, each profile maintains its own separate cookie storage.
Same-site policies and other security restrictions can still apply across tabs. A website cannot access cookies set by another website due to the same-origin policy, regardless of whether you're on the same tab or different tabs. This security measure prevents malicious sites from stealing authentication cookies or other sensitive data from other websites.
If you want to isolate cookies between tabs for privacy or testing purposes, you would need to use Incognito windows or separate Chrome profiles, as there's no built-in feature to limit cookie sharing between regular tabs.