Quick answer
A third-party cookie is a cookie set by, and sent to, a domain other than the site shown in the address bar, typically by an embedded ad, tracking pixel, social button or widget. It lets that other domain recognise the same browser across different sites.
What is a third-party cookie?
A cookie is first-party or third-party only by one rule: does the domain that sets it match the site in the address bar?
- First-party: set by the site you are visiting. Used for logins, carts and preferences.
- Third-party: set by another domain whose content is embedded in the page, such as an ad server, a tracking pixel, a social share button or a video player. Because the same third party is embedded on many sites, its cookie can recognise one browser across all of them.
To be sent in a cross-site context, a cookie must be marked SameSite=None; Secure.
A sample page
A visitor opens shop.example.com/product (sample):
| Cookie set by | Purpose | Type |
|---|---|---|
| shop.example.com | Cart and login session | First-party |
| shop.example.com | Language preference | First-party |
| ads.example.net (pixel) | Retargeting across sites | Third-party |
| video.example.org (embedded player) | Player settings and tracking | Third-party |
Only the last two disappear when a browser blocks third-party cookies. The cart and login keep working.
Browser status
| Browser | Default behaviour |
|---|---|
| Safari | Blocks third-party cookies |
| Firefox | Isolates them per site (Total Cookie Protection), so they cannot track across sites |
| Chrome | Allows them by default; users can block them. Google said in 2025 it would keep this user-choice approach instead of phasing them out |
What breaks without them
- Breaks: cross-site retargeting audiences, view-through conversion tracking, frequency capping across sites, some embedded logins and comment widgets.
- Keeps working: your own login, cart and preferences; analytics that runs on your domain or writes no cookie; server-side conversion events.
Analytics without third-party cookies
Prefer measurement that does not depend on them: first-party data, server-side events and cookieless counting. TapCub's website script writes no cookie and no local storage, so browser cookie blocking does not change its visitor counts. See cookieless analytics and first-party data strategy.
See also
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Solutions Engineer
Covers SDKs, API integrations, and data implementation, with an emphasis on validation, system interoperability, and troubleshooting.