Link decoration and privacy
Link decoration is the practice of appending query parameters or fragments to a URL — click identifiers, user IDs, or attribution tokens — so information travels with the user as they navigate between sites. It can serve legitimate campaign measurement but is also used to bridge cross-site tracking once cookies are restricted. Browsers like Safari and Firefox now strip known tracking parameters in some contexts. This page is educational.
How link decoration works
When a user clicks a link, any data placed in the URL's query string or fragment travels to the destination. Marketers use this for legitimate measurement — UTM parameters tag a campaign source — but the same channel can carry a per-user click identifier that lets a third party re-identify the user on the next site, effectively bridging the gap left by restricted cookies. The distinction is between first-party context you set for your own measurement and cross-site identifiers designed to follow a person.
How browsers are responding
Safari's Intelligent Tracking Prevention can cap or downgrade storage when a navigation appears to use link decoration for tracking, and both Safari and Firefox strip known tracking query parameters (like certain click IDs) in private windows or with strict protection enabled. The result: identifiers you rely on may not survive the trip. Build measurement on first-party UTM-style parameters you control and on server-side joins you own, rather than third-party click IDs that browsers may remove.
Keep decorated parameters to the minimum your own reporting needs.
- URL parameters carry data across cross-site navigation
- Browsers strip known tracking parameters in some modes
- Prefer first-party UTM parameters you control
How it appears in analytics and logs
If inbound URLs carry click IDs that vanish in some browsers, link-decoration stripping is at work; rely on first-party parameters you control, not third-party IDs.
Diagnostic use case
Understand how appended URL parameters carry identifiers across navigation, and why browsers increasingly remove known tracking parameters by default.
What WebmasterID can help detect
WebmasterID reads first-party campaign parameters (UTMs) you set yourself, rather than depending on third-party click identifiers browsers may strip.
Common mistakes
- Depending on third-party click IDs that browsers may strip.
- Conflating first-party UTM tags with cross-site identifiers.
- Decorating links with more identifiers than reporting needs.
Privacy and accuracy notes
This page is educational, not legal advice. Decorating links with identifiers can extend tracking; minimise to the campaign parameters you actually need.
Related pages
- Referrer trimming and privacy
Referrer trimming is the browser practice of limiting what the Referer header (and document.referrer) reveals on navigation. Modern browsers default to the strict-origin-when-cross-origin Referrer Policy, which sends the full URL only same-origin and just the origin (scheme + host) cross-site, and sends nothing when downgrading from HTTPS to HTTP. This narrows referrer data analytics can collect. This page is educational.
- Safari ITP and analytics privacy
Intelligent Tracking Prevention (ITP) is WebKit's privacy feature that partitions and limits storage to stop cross-site tracking in Safari. It blocks third-party cookies, caps script-set first-party cookie lifetimes, and constrains other client-side storage. This page summarises ITP's documented behaviours and what they mean for measuring audiences.
- Bounce tracking mitigation
Bounce tracking (or redirect tracking) routes a user through a tracker's domain mid-navigation so the tracker can set or read its own first-party storage and link the visit across sites. Browsers now detect this pattern and purge the state. This page explains the technique and the mitigations Safari and Chrome apply.
- Campaign links
First-party campaign parameters you set and control.
Sources and verification notes
- WebKit — Tracking Prevention (link decoration handling)Primary documentation on ITP's handling of link decoration.
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.