VAST Inspector
Test and debug VAST tags with full XML inspection, playback simulation, and real-time event tracking—all in one tool. Built for QA teams and video operations specialists, this tool uses the Google IMA SDK to simulate real-world playback and surface issues in tag structure or delivery. Paste your VAST tag to view formatted XML, preview creative playback, and monitor SDK events like load, start, and complete in real time. It’s ideal for troubleshooting wrappers, verifying third-party tags, or confirming tracking pixels. Everything runs client-side for speed and privacy during development and testing.
Load a video tag and preview its structure and playback signals in one place.
What you can do here
- Confirm a tag resolves and plays as expected.
- See wrapper depth and tracking events quickly.
- Share a clean breakdown with teammates.
Before you start
- Paste a VAST URL or XML.
- Use an example if you want to test the UI.
About VAST Inspector
The VAST Inspector allows QA teams to simulate video tag playback using the Google IMA SDK and see errors, tracking events, and inline XML content instantly.
Use it to analyze VAST tags or URLs, validate versions, and inspect wrapper chains before ad delivery.
Best uses for VAST Inspector
- Confirm a tag resolves and plays as expected.
- See wrapper depth and tracking events quickly.
- Share a clean breakdown with teammates.
How to use VAST Inspector
- Paste a VAST URL or raw XML into the editor.
- Click 'Inspect' to launch a simulated player with event tracking.
- Review impressions, errors, quartiles, and XML structure side-by-side.
What to paste in
- Paste a VAST URL or XML.
- Use an example if you want to test the UI.
What you should see
- Parsed XML with key fields summarized.
- Event log showing playback and errors.
Example checks
These are simple checks you can run when you want a real sample and a clear result to compare against.
Paste a VAST URL or XML.
Why run it: Confirm a tag resolves and plays as expected.
What to look for: Parsed XML with key fields summarized.
Use an example if you want to test the UI.
Why run it: See wrapper depth and tracking events quickly.
What to look for: Event log showing playback and errors.
VAST Tags Explained: How Video Ad Delivery Works from Tag to Playback
Understanding the VAST Specification
VAST, the Video Ad Serving Template, is an XML-based standard developed by the Interactive Advertising Bureau (IAB) Tech Lab. It defines how video ad servers communicate with video players, specifying the structure for delivering video ads, tracking impressions, and reporting playback events. Since its introduction, VAST has become the universal language of video advertising, enabling interoperability between ad servers, demand-side platforms, supply-side platforms, and video players across the programmatic ecosystem.
A VAST tag is essentially a set of instructions for a video player. It tells the player where to find the video creative file, what tracking pixels to fire at specific playback milestones (start, first quartile, midpoint, third quartile, complete), where to send impression and click-through data, and how to handle errors. The specification supports multiple creative formats, companion ads, and verification scripts, making it a comprehensive framework for video ad delivery.
The VAST specification has evolved through several versions. VAST 2.0 introduced the foundation, VAST 3.0 added support for ad pods and skippable ads, and VAST 4.0 and 4.1 introduced mezzanine file support, universal ad IDs, and improved verification mechanisms. Each version builds on the previous, and modern ad servers typically support multiple versions to maintain backward compatibility with different player implementations.
Wrapper Chains and How Tags Resolve
One of the most important concepts in VAST is the distinction between inline tags and wrapper tags. An inline VAST response contains the actual creative and media files that the player will render. A wrapper response, by contrast, does not contain media files — instead, it contains a VASTAdTagURI element that points to another VAST endpoint. The player must follow this chain of wrapper redirects until it reaches an inline response with playable media.
In programmatic advertising, wrapper chains are common because multiple parties in the ad supply chain need to add their tracking and verification. An ad might originate from an advertiser's ad server, pass through a demand-side platform's VAST wrapper (which adds tracking pixels), then through a supply-side platform's wrapper (which adds its own reporting), before finally reaching the publisher's video player. Each hop adds tracking but also adds latency and potential points of failure.
Debugging wrapper chains is one of the most frequent tasks for video ad operations teams. A tag that fails to render might be failing at any point in the chain: a wrapper might point to an unreachable URL, an intermediate response might return invalid XML, or the final inline response might lack required media files. Without a systematic way to inspect each hop in the chain, diagnosing these issues requires manually following URLs and parsing XML at each step — a time-consuming and error-prone process.
Common VAST Issues and How to Diagnose Them
The most common VAST issues fall into several categories. Tag loading failures occur when the VAST URL is unreachable, returns a non-XML response, or times out. XML parsing errors happen when the VAST response is malformed — unclosed elements, invalid characters, or incorrect nesting. Media file issues arise when creative URLs are broken, formats are unsupported by the player, or file sizes exceed player limits.
Tracking discrepancies — where impression or event counts do not match between parties — often trace back to VAST configuration issues. A tracking pixel URL that contains unescaped special characters will fail silently. A wrapper that does not properly pass through the inner response's tracking elements will cause undercounting. An error handler that fires before the player attempts to load media will generate false error reports.
A VAST inspector tool that can load a tag, follow wrapper chains, parse the resulting XML, and simulate playback events provides the visibility needed to diagnose these issues efficiently. By showing the full chain, the parsed structure, and the sequence of events in a single view, it transforms a multi-step debugging process into a quick visual inspection.
Troubleshooting
What to look for
- Parsed XML with key fields summarized.
- Event log showing playback and errors.
Common issues
- Private URLs may fail if they require auth.
- Some tags block automated requests.
Best practices
- Include the full URL (with https://) for best results.
- If a fetch fails, confirm the endpoint is publicly reachable.
- Some hosts block automated requests; try a different URL if needed.
Related tools
More tools in the vast tools category.
- VAST Wrapper Visualizer - Paste a VAST tag and map the wrapper chain visually from publisher request to final inline creative. This debugger is built for video QA, ad ops, and CTV teams that need to see wrapper ownership, hop order, and depth risk quickly before escalating an issue to an ad server or SSP.
- VAST Wrapper Latency Analyzer - Measure latency for each VAST wrapper request and flag the hops most likely to push a browser or CTV player beyond its timeout budget. This tool is built for ad ops teams debugging slow supply paths and late inline responses.
- Redirect Chain Analyzer - Trace redirect chains for VAST tags, click trackers, and ad-request URLs with hop-by-hop status codes and latency. Use it when you need to know exactly where an ad-tech URL ends up before it reaches the player or landing page.
- VAST Error Code Explainer - Enter a VAST error code and get a plain-language explanation plus the first troubleshooting steps to take. Useful for QA, CTV support, and partner escalations when the player exposes an error number but not enough context to act quickly.
Related reading
More specific pages for the exact jobs this tool supports.
VAST Error 100: XML parsing error
Parse failures, bad markup, encoding issues, and malformed VAST XML.
VAST Error 101: VAST schema validation error
When the VAST is XML but still breaks the declared schema rules.
VAST Error 102: VAST version not supported
Version mismatch between the ad response and the player or SDK.
VAST Error 200: Trafficking error
Unexpected ad type, unsupported response type, or bad trafficking assumptions.
VAST Error 201: Video player expecting different linearity
When the player expects linear or non-linear behavior and receives the opposite.
VAST Error 202: Video player expecting different duration
Creative duration does not fit what the player or placement expects.
VAST Error 204: Ad category required but not provided
Required category metadata is missing from the response.
VAST Error 400: General linear error
General linear playback error with no narrower media file explanation.
Frequently asked questions
Is it free to use?
Yes. Core tools are free and accessible without signup.
Does it upload my data?
This tool makes server-side fetches to the URLs you provide so results can be rendered. We do not store the fetched content beyond the request.
What if I spot a bug?
Please reach out via the Contact page with a reproduction example.
Does it make network requests?
Yes, only when you provide a VAST URL for analysis.
Which VAST versions are supported?
VAST 2.x through 4.x with automatic detection.
Why might schema validation fail?
Macros or strict XSD constraints can fail in some environments.
Helpful links
Standards & references
Official specs that inform how this tool interprets data.