What is VAST Tag Tester?
VAST Tag Tester is a free online tool for validating video ad tags against the IAB VAST 2.0–4.3 specification. Paste a VAST URL or raw XML, and it instantly parses the response, resolves wrapper chains up to 5 hops deep, and surfaces errors and warnings (e.g. error 100 XML parse failure, 303 wrapper limit exceeded) before they hurt ad delivery. It also audits all tracking pixels (impression, click, and quartile events) with vendor detection and live HTTP status checks, and analyzes MediaFile elements for codec, bitrate, resolution, and MIME type. No account or sign-up required — built for ad ops teams, publishers, agencies, and programmatic advertising engineers who need to catch ad errors before they reach real viewers.
