What is VAST & How to Test VAST Tags

What is VAST? – An Overview

VAST (Video Ad Serving Template) is a standardized XML-based protocol developed by the Interactive Advertising Bureau (IAB) to facilitate the delivery of video advertisements across a wide variety of media players, devices, and platforms. It acts as a bridge between ad servers and video players, ensuring consistent communication of ad metadata, creatives, and tracking requirements regardless of the playback environment — whether on desktop, mobile, connected TV (CTV), or in-app video. At its core, VAST defines a structured XML response that includes information about the video ad creative (such as file URLs, durations, and formats), companion ads, error reporting, and detailed tracking events (e.g., impressions, quartile completions, clicks, mutes, pauses, and more). This allows video players to interpret and render ads correctly while also reporting performance metrics back to advertisers.

VAST supports multiple types of ad formats including:

• Linear ads: These are standard in-stream ads (like pre-roll, mid-roll, or post-roll) that interrupt or precede video content.
• Non-linear ads: These typically overlay on top of video content without fully interrupting playback.
• Companion ads: Static or rich media assets (such as banners) displayed alongside the main video ad to increase engagement or visibility.

Key milestones in VAST specification:

• VAST 3.0: Introduced support for ad pods (sequential ads), better error reporting, and improved tracking.
• VAST 4.0 and beyond: Added separation of media files from metadata via wrappers, support for server-side ad insertion (SSAI), verification APIs (via Open Measurement), and conditional ad declarations to improve creative load efficiency and fraud detection. VAST also integrates with other IAB standards such as VPAID (Video Player-Ad Interface Definition) for interactive ads, and SIMID (Secure Interactive Media Interface Definition) for secure communication between ads and players. Because VAST is an open and extensible standard, it enables interoperability across ad tech systems — allowing publishers, ad networks, and DSPs (demand-side platforms) to streamline video ad workflows without needing proprietary integrations. In modern digital advertising, VAST is fundamental to scalable, measurable, and cross-platform video ad delivery — making it a cornerstone of programmatic video, CTV, and in-app video monetization.

• How to use VAST? Publishers or ad ops teams embed a VAST tag (URL or XML) in their video player or ad server configuration. The player fetches the VAST tag, parses the XML, and displays the ad as specified.
• What does a VAST tag contain? A VAST tag includes information about the ad creative (video file, companion banners), tracking URLs for impressions and events, duration, click-through URLs, and more.
• Where is VAST used? VAST is used in online video players, CTV/OTT apps, mobile apps, and any environment that supports video ad playback. It is supported by most major ad servers and publisher video players.