A cookie is a small text file that a website places in a user's browser to store information about their session, preferences, and behaviour. When a user visits a website, the server can set a cookie on the browser; on subsequent visits, the browser sends that cookie back to the server, allowing the site to "remember" the user. Cookies persist for a defined duration — session cookies expire when the browser closes, while persistent cookies remain for days, months, or years depending on their settings.
Two key types matter for ecommerce:
- First-party cookies: Set by the website domain itself (yourbrand.com). Used for session management, cart persistence, login state, and on-site personalisation.
- Third-party cookies: Set by a different domain (e.g., Facebook Pixel, Google Ads) embedded on your site. Used for cross-site tracking, ad retargeting, and attribution across the web. These are being deprecated by major browsers.
Why Cookies Matter for Ecommerce
Cookies are the mechanism behind most ecommerce personalisation, A/B testing, cart persistence, and ad attribution. Without cookies:
- Users would lose their shopping cart on every page refresh
- A/B testing tools couldn't maintain consistent variant assignment — users would see different variants on each visit
- Retargeting ads wouldn't know who abandoned their cart
- Analytics tools couldn't track return visits or session duration
For Indian D2C brands, first-party cookies are increasingly critical as third-party cookies phase out. Google's Chrome deprecation of third-party cookies (delayed multiple times, now in flux) is pushing ecommerce brands to build direct data relationships with customers — capturing email, phone, and purchase history through first-party means.
Cart persistence cookies alone have measurable revenue impact. When a user adds products to their cart, leaves, and returns on the same or different day, a persistent cart cookie recovers the session where it was abandoned — reducing the friction of starting over and increasing checkout completion.
Real-World Example
A Shopify brand selling premium notebooks uses a first-party cookie to remember cart contents for 30 days. Analytics shows that 12% of their purchasers add to cart, leave the site, and return to complete purchase within 7 days. Without cart persistence cookies, these buyers would return to an empty cart and 60–70% would not bother rebuilding it — resulting in a significant portion of purchases being lost. The 30-day cookie window costs nothing to maintain and preserves approximately ₹1.8 lakh/month in revenue that would otherwise require re-acquisition through retargeting ads.
A/B testing tools (including CustomFit.ai) use a first-party cookie to store the variant a user has been assigned to. This ensures the same user always sees the same variant across multiple sessions — preserving test integrity and preventing the jarring experience of seeing different versions of the site on repeat visits.
How to Improve / Optimize Cookie Strategy
- Audit your cookie usage and expiration settings. Session cookies expire immediately; persistent cookies should be set long enough to cover your typical customer journey. A 7-day cookie on a brand with a 14-day consideration cycle means returning buyers lose their session half the time.
- Migrate to first-party tracking as third-party cookies sunset. Set up server-side tracking (sending events from your server rather than the browser), capture email at more touchpoints, and use your own first-party analytics alongside platforms that rely on third-party cookies.
- Be transparent about cookie usage. A clear cookie consent banner (GDPR-aligned, and increasingly expected by Indian consumers too) that explains what each cookie does builds trust. Blanket "we use cookies" notices with no opt-out choice are both bad UX and increasingly non-compliant.
- Test cookie consent banner design. The design and copy of your consent banner affects how many users accept or reject cookies. A/B test placement, language, and button design — optimising for consent rate without compromising honesty.
- Use cookie fallbacks for logged-in users. For customers with accounts, store their cart, wishlist, and experiment assignment server-side (linked to their user ID) rather than relying solely on browser cookies. This survives browser clearing and cross-device access.
Cookies in A/B Testing
A/B testing depends on cookies to maintain consistent variant assignment. When a user is assigned to Variant B, their assignment is stored in a first-party cookie. On every subsequent page load, the testing tool reads the cookie and serves Variant B consistently. Without this mechanism, users would see random variants on each visit — producing invalid test data and a confusing user experience. Server-side testing stores variant assignment in a database keyed to user ID or session ID, providing a more durable alternative to cookie-based assignment.
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