Video Ad Serving Template (VAST)

An IAB XML specification that tells a video player which ad to play, where to fetch it, and which tracking events to fire.

By Brandon MinaCEO, BrandPilot AIUpdated November 2026

Short answer

Video Ad Serving Template (VAST) is an IAB Tech Lab XML specification that tells a video player which ad to play, where to fetch the media file and which tracking events to fire. By standardizing communication between ad servers and players, VAST lets video ads run consistently across publishers, devices and platforms.