Open Developer Tools → VAST Testing Lab and paste a VAST URL. The tool inspects advertising XML and can show a native preview for supported media.
Three levels of confidence
- XML exists: the server returns a VAST response and the parser finds an ad.
- Media playable: a browser can decode the advertised MP4.
- Advertising workflow verified: a true VAST player plays the ad, honors the ad-break flow and reports tracking events.
Only the third proves real advertising integration. The built-in native preview is not an automated JW Player, Bitmovin or Roku certification suite.
Google IMA external test
Use Google Video Suite Inspector, paste your VAST URL and watch the full ad event log. For a two-ad pod, verify both play in order, including tracking and transition to main content.
Metrics warning
A third-party tester may generate live ad events. Don't repeatedly test against production tags and then assume every event is an audience impression.