What is a walled garden in advertising?
Why does a walled garden matter for measurement?
The data stays inside. The Competition and Markets Authority (CMA) reported that Google and Facebook do not let advertisers or independent measurement and attribution providers collect user-level data from ads on their own inventory, "ie in the walled garden"1. Its example of how this works on a social media platform such as Facebook: the advertiser sets its bidding strategy, and the platform decides which ad to show, delivers it and provides verification and attribution data back1.
So the platform sells the ad and marks the result. That is not proof the numbers are wrong. It does mean that platform ROAS is the platform's view of its own work.
The CMA also notes that walled-garden platforms can track users across devices and sessions, which lets them attribute actions more accurately than third parties1. Both things are true: more data, less independent checking.
What can you check outside the wall?
- Your own sales. Shop orders and revenue do not depend on any platform's report.
- Experiments. A conversion lift study randomly splits users into a group that can see the ads and a control group that cannot. It is still run by the platform, but it compares against a control.
- Model choices. Meta's incremental attribution option optimises for conversions its model predicts the ads caused. Still the platform's model, so ask how it was checked.
Which method answers which question is laid out in MMM vs MTA vs incrementality tests.
Our view: platform numbers are evidence, not a verdict, and a budget decision needs at least one check the platform does not grade itself.
Easily confused with
Walled garden vs First-party data
Every brand has its own customer data. A walled garden is about a platform keeping its users' data inside its own system.
Buzzword alert
"We can't see inside the walled garden, so we go by platform data"
Usually means: no independent check was planned.
Ask: what do our own sales show when this spend changes?
"Walled-garden data is the most accurate"
Usually means: the platform has more data about its users, which is not the same as an independent result.
Ask: has this been compared with a control group?
FAQ
Which platforms are walled gardens?
Is a closed ecosystem the same as a walled garden?
Close to it. The CMA's definition calls a walled garden "a closed ecosystem"1. A walled-garden platform is one that works this way.
Does a walled garden mean the platform's numbers are wrong?
No. It means the platform reports on its own ads. Treat those numbers as one view and check them against something it does not control.
Let’s find what’s actually working.
Next step. See how much of your reported ROAS holds up on your own assumptions. Use the Is your ROAS real? calculator.