VAST (Video Ad Serving Template)

The universal, de facto open standard for video ad serving adopted across the entire digital video and CTV advertising ecosystem

VAST (Video Ad Serving Template) is an XML-based specification developed and maintained by the IAB Tech Lab that standardizes how video ads are served from ad servers to video players. First introduced in 2008, VAST defines a universal communication protocol that allows any compliant ad server to deliver video ads to any compliant video player, eliminating the need for custom integrations between publishers and advertisers. The standard has evolved through multiple versions — from VAST 1.0 through VAST 4.x — progressively adding support for features like interactive ads, viewability measurement, server-side ad insertion (SSAI), and advanced CTV/OTT delivery. VAST plays a foundational role in the programmatic video advertising ecosystem. It works in conjunction with other IAB standards such as VPAID, SIMID, and VMAP to provide a comprehensive framework for video ad delivery, interactivity, and measurement. The standard is particularly critical in the CTV and streaming space, where it enables ad pods, dynamic ad insertion, and compliance with platform-specific requirements. VAST 4.x introduced significant improvements including support for server-side ad insertion, universal ad ID, and improved error reporting. As an open, royalty-free standard governed by the IAB Tech Lab, VAST is not a commercial product but rather an industry specification adopted universally by ad servers (Google Ad Manager, FreeWheel, SpotX), DSPs, SSPs, and video players worldwide. Its ubiquity makes it the de facto lingua franca of video advertising, and compliance with VAST is considered a baseline requirement for participation in the digital video and CTV advertising marketplace.