Annotations are short notes pinned to a date on a report's timeline. They record anything that could explain a change in the data: a site migration, a tracking fix, a pricing change, a campaign launch or a known search algorithm update. Without them, teams spend hours rediscovering why a line moved, or draw the wrong conclusion from it.
Where annotations live
Universal Analytics had annotations; GA4 launched without them and Google added native annotations to GA4 reports in 2025. Search Console has also added custom annotations to its Performance report. Availability and features can vary, so many teams also keep a shared change log in a spreadsheet or their dashboard tool as the source of truth.
What to annotate
Annotate anything that changes what the data means or what produces it.
- Tracking changes: new key events, tag fixes, consent banner launches, timer changes
- Site changes: migrations, redesigns, new sections, large redirects
- Marketing changes: campaign launches, pricing updates, product launches
- External events: confirmed Google core updates, holidays, outages
Writing useful annotations
Keep each note specific: what changed, where, and who to ask. 'Moved /docs to docs subdomain, 301s live, owner: platform team' is far more useful than 'docs change'.
Agree on who adds annotations and when. The simplest rule is that whoever ships a change that could affect tracking or traffic adds the note on the day it goes live, in the shared log and in the tools that support it. A short weekly check by the analytics owner catches anything missed.
Example
Explaining a drop six months later
Suppose Gildenrow, an onboarding software company, sees engagement rate fall one spring. An annotation from that week reads: 'Removed scroll from key events'. The drop is a definition change, not a content problem, and the review takes minutes instead of a week.
Common mistakes
Annotating only wins
Tracking breaks and outages are the annotations that save the most time later.
Keeping notes in one person's head
Use a shared place so the context survives team changes.
Questions
Annotate confirmed updates from Google's Search Status Dashboard, with the start and end dates, so you can compare them with your own changes.
