VAST Tags Explained: From Protocol Structure to Production Practice
VAST Tags Explained: From Protocol Structure to Production Practice VAST (Video Ad Serving Template) is the XML specification maintained by the IAB Tech Lab for serving video ads. The current major version is VAST 4.2, released in 2021, though VAST 2.0 and 3.0 responses are still common across legacy supply paths — which is why the first step in any debugging session is confirming which version you're actually looking at. The spec exists to solve one problem: letting an advertiser's creative play and get measured correctly inside a player it has no control over. Every design decision in the spec follows from that constraint. InLine vs. Wrapper: the core structural split A VAST response starts with a <VAST version="4.2"> root node containing one or more <Ad> elements. Each <Ad> is either an <InLine> or a <Wrapper> — there's no third option. An <InLine> is a terminal response carrying the actual playable creative. Under ...