Storage partitioning and CHIPS
Storage partitioning keys client-side storage (cookies, localStorage, caches) by the top-level site, so an embedded third party cannot use the same storage to recognise a user across different sites. CHIPS (Cookies Having Independent Partitioned State) lets a cookie opt into per-site partitioned storage. This page explains both and their effect on analytics.
What partitioning does
Historically, an embedded third party could read and write the same storage on every site it appeared on, enabling cross-site recognition. Storage partitioning changes the key so storage is scoped to the combination of the embedded origin and the top-level site. The same widget on two different sites now gets two separate storage partitions and cannot link a user between them.
- Storage is keyed by top-level site, not just origin
- Cross-site recognition via shared storage is blocked
- Applies across cookies and other storage mechanisms
Where CHIPS fits
CHIPS provides a controlled exception for legitimate per-site use of third-party cookies: a cookie set with the Partitioned attribute gets its own jar tied to the top-level site, so it works within that site but cannot be reused to track across sites. This supports use cases like embedded sub-resources or per-site session state without re-enabling cross-site tracking.
How it appears in analytics and logs
Missing cross-site continuity for an embedded tool often reflects storage partitioning, not a bug — its storage is now separate per top-level site.
Diagnostic use case
Understand why embedded or third-party analytics may no longer share state across sites, and how a partitioned (CHIPS) cookie can still function within a single top-level site.
What WebmasterID can help detect
WebmasterID measures first-party within a single site, so storage partitioning does not degrade its counts — it never depended on cross-site shared storage.
Common mistakes
- Assuming a partitioned cookie still works across sites.
- Treating partitioning as if it blocks first-party storage.
- Confusing CHIPS opt-in with unrestricted third-party cookies.
Privacy and accuracy notes
This page is educational and not legal advice. Partitioning limits cross-site recognition but does not by itself establish a lawful basis for any processing.
Related pages
- Third-party cookie deprecation
Third-party cookie deprecation refers to browsers blocking or phasing out cookies set on domains other than the site a user is visiting. Safari and Firefox already block them by default; Chrome has documented its own plans and shipping changes. This page explains the state of play and what it means for analytics that relied on cross-site cookies.
- Chrome Privacy Sandbox and analytics
The Privacy Sandbox is a set of Chrome web-platform APIs intended to support advertising and measurement use cases without cross-site tracking of individuals. It includes interest-based targeting, conversion measurement, and anti-abuse APIs that return aggregated or noised results rather than per-user identifiers. This page maps the pieces and what they mean for analytics.
- Essential vs non-essential cookies
Under the EU ePrivacy Directive, storing or reading information on a user's device is allowed without consent only when it is strictly necessary to provide a service the user explicitly requested. Everything else — including the vast majority of analytics, advertising, and personalisation cookies — is non-essential and requires prior, informed consent. This page explains the test and where analytics usually lands.
- Privacy-first analytics
First-party measurement unaffected by partitioning.
Sources and verification notes
- Google — CHIPS (Cookies Having Independent Partitioned State)Specification and behaviour of partitioned cookies.
- MDN — Cookies Having Independent Partitioned State (CHIPS)How the Partitioned attribute and storage partitioning work.
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.