VAST error codes / General
VAST error 900: Undefined error
Short answer: An error the player could not classify.
What it means
A fallback the player fires when it cannot map a failure to any specific code. It tells you something broke, not what.
Common causes
- Player-specific failure with no matching code
- A bug or unexpected state in the player
How to fix it
Reproduce with the raw tag in the validator and the inspector, and a 900 usually resolves into a concrete structural problem once you see the XML.
VAST error codes are runtime buckets emitted by the player. They tell you where the failure happened, not which line of XML caused it. Paste the raw tag into the validator to map this code onto the exact element and rule.
Related error codes
Debug this tag now
Validate the XML, follow the wrapper chain, or check it in CI before launch:
# CLI: exits non-zero on errors, ideal for pipelines
vastlint check creative.xmlUse the right tool for this failure
If you already have the resolved XML, run a pure spec check. If you only have a live tag URL, test that endpoint first. If the failure happens in the wrapper chain, inspect each hop.