Docs
Fallback creatives
What PubTrust paints into a slot after it blocks the creative that was there, and how it chooses.
What is a fallback creative?
The stand-in PubTrust paints into a slot after blocking the creative that was there, so a block never leaves a visible hole. It is overlaid inside your slot element at the slot's measured dimensions, and only when both the Site and the policy that fired are in Block — Monitor mode never paints one.
What can a fallback be?
| Kind | Renders as |
|---|---|
| Image | An image served from the PubTrust CDN, drawn at the slot's dimensions. |
| HTML | Your markup inside an iframe with an empty sandbox attribute: no scripts run, no forms submit and nothing in it can navigate your page. |
| Colour | A plain block in the colour you set. |
| Blank | Nothing. The slot stays empty but keeps its box. |
Any kind except Blank can carry a click-through URL, which opens in a new tab with rel="noopener noreferrer nofollow". HTML fallbacks are sanitised when they are saved, and the sandbox means that even markup which slipped past the sanitiser could not execute — a fallback must never become the vulnerability PubTrust was installed to prevent.
Which fallback is chosen?
The closest fit, in a fixed order. A 300×250 house ad inside a 728×90 leaderboard looks worse than an empty slot, so size fidelity comes before branding.
- The fallback attached to the policy that fired, if it has the slot's exact size or no fixed size.
- Otherwise, the first fallback whose width and height exactly match the slot.
- Otherwise, the first responsive fallback — one with no declared dimensions.
- Otherwise, the policy's own fallback, even though its size differs.
- Otherwise, the Site's default fallback. If there is none, the slot is left empty.
Does a fallback shift my layout?
No. The blocked creative is hidden with visibility:hidden, never display:none, so the slot keeps its box, and the fallback is absolutely positioned inside the slot at the dimensions measured before the creative was removed. If your slot element has position: static, the tag sets position: relative on it so the overlay has something to position against. If the tag stands down, the overlays and the stylesheet it added are removed.
Where are fallbacks configured?
Per Site: attach a fallback to a policy, keep fallbacks for specific sizes, and set a Site default. They are delivered inside the Site's tag configuration, so choosing one needs no network request at block time; an image fallback loads its image from the CDN.