First-Party Cookie

A first-party cookie is a small piece of data stored in the browser for the domain the visitor is on. Stores use first-party cookies to keep carts, hold logins and recognize returning visitors.

How is it different from a third-party cookie?

	First-party cookie	Third-party cookie
Whose domain	The site in the address bar	Another domain loaded on the page
Typical uses	Carts, logins, on-site analytics, recognizing a returning visitor	Following a visitor across unrelated sites
Visible to other sites	No	Yes, wherever that third party is loaded

Vendor tools can write first-party cookies too. Klaviyo's script writes __kla_id on your domain, for example. The label refers to the domain the cookie belongs to.

How long does a first-party cookie last?

Being first-party doesn't guarantee a long life. The browser decides, and who wrote the cookie matters.

• Set by script. Klaviyo's cookie documentation says __kla_id is set for 2 years and browsers can shorten that. Safari's ITP deletes script-set cookies after 7 days of browser use without interaction with the site.
• Set by a server. A server-side cookie, written in the HTTP response, isn't covered by that script rule. It has its own exceptions in Safari, and Brave caps server-set cookies at 6 months according to Klaviyo's docs.
• In Chrome. Klaviyo's docs give a limit of up to 400 days.

What can a first-party cookie do for a store?

• Keep the cart in the browser where it was built.
• Recognize the same browser on a later visit, which helps tie the visit to a known profile. This is the basis of device recognition.
• Support on-site analytics that isn't shared with other sites.

What can't it do?

A first-party cookie can't cross devices. A shopper who starts on a laptop and opens your email on a phone arrives with a separate set of cookies, so the phone may show an empty cart. That's cross-device cart abandonment, and it takes an email click or login plus a saved cart to fix.

It also can't name someone on its own. A cookie only recognizes a person if they gave their details at some point and the cookie got linked to them. Reaching beyond that is the territory of identity networks, which match visitors against shared cross-brand graphs.

How does this relate to reOtter?

reOtter works with first-party information only. It recognizes people who've already given your brand their details, without a third-party network, in a record that doesn't depend on a browser cookie surviving. Strangers aren't identified.

Key takeaways

• First-party describes whose domain a cookie belongs to, and its lifespan depends on the browser and on who set it.
• Safari can delete script-set first-party cookies after 7 days of browser use without interaction with the site.
• A first-party cookie stays in one browser, so it can't restore a cart on a second device by itself.

See how reOtter restores the cart → Abandoned cart recovery