VAST error code
301 — Timeout of VAST URI
What the spec says
The player requested the URI in a wrapper and the response did not arrive within its timeout.
What actually causes it
- A slow ad server at some hop in the chain.
- Too many wrapper hops, each adding latency until the cumulative time exceeds the budget.
- Geographic distance — a chain that resolves comfortably in one market timing out in another.
- A player timeout that is simply short, which is common in CTV.
How to fix it
Time each hop individually to find the slow one. If total latency is the problem rather than a single bad server, the answer is fewer hops — every wrapper you remove buys back its full round trip.
To see whether a tag would hit this before it runs, paste it into the VAST validator. It reads the XML and reports the conditions that map to this code.
Related codes
Code definitions from the IAB Tech Lab VAST 4.3 specification. Causes and fixes are practitioner guidance, last verified July 2026.