What does VAST error code 303 mean?

303 is a wrapper error: 'No ads VAST response after one or more Wrappers'. The redirect chain resolved to an empty VAST document — a no-fill. The XML is valid; the upstream simply had no ad to serve, so look at demand and targeting, not the markup.

Where do VAST error codes actually come from?

The player substitutes the numeric code into the [ERRORCODE] macro of the ad's URI and fires it as a tracking pixel. The codes and their meanings are defined in the IAB Tech Lab VAST 3.0 and 4.x specifications.

What is the difference between VAST error 100 and 101?

100 is an XML parsing error — the response is not well-formed, so it will not parse at all. 101 is schema validation — the XML parses but does not match the VAST schema, for example a missing required element or a misplaced attribute.

Does this cover VPAID error codes as well as VAST?

Yes. 901 is the general VPAID error, alongside the full VAST set. VPAID is deprecated in favour of SIMID and OMID, but 901 still appears when a legacy interactive creative fails to initialise or run.

Why is my error code missing from the lookup?

Only codes 100 through 901 are part of the standard IAB VAST/VPAID range. Codes outside it are typically custom to a specific SDK, player, or ad server, so their meaning lives in that vendor's own documentation.

Can I look up a code without exposing my ad tag?

Yes. The complete code table is bundled into this page, so typing a number or pasting an [ERRORCODE] value is matched locally on your device. No VAST response, ad tag, or error string is sent to ArrayKit.

VAST Error Code Lookup

Search every IAB VAST and VPAID error code to find its official meaning, category, and likely cause — matched right in your browser.

The VAST Error Code Lookup bundles the full IAB code table into the page, so every search and lookup runs on your device. The error codes, [ERRORCODE] values, and VAST responses you paste are never uploaded to ArrayKit.

Open the VAST Validator

About VAST Error Code Lookup

The VAST Error Code Lookup is a searchable reference of every IAB VAST and VPAID error code — from 100 XML parsing and 101 schema validation through the 300-series wrapper codes, the 400-series linear media-file failures, non-linear and companion errors, and the 900/901 undefined and VPAID errors. Type a number or pick a category to see the official meaning, the class it belongs to, and the most likely cause and fix. It is built for ad-ops engineers, publishers, and DTC teams staring at an [ERRORCODE] macro in an <Error> beacon and trying to work out why a video ad did not render. The full table is bundled into the page, so every lookup happens on your device — no error string, ad tag, or VAST response is ever uploaded to ArrayKit.

Features

Every standard IAB VAST 3.0 and 4.x error code, from 100 through 901, in one table
Search by number, keyword, category, or any text from the error's meaning or cause
Filter by class: Parsing, Trafficking, Wrapper, Linear, NonLinear, Companion, and VPAID
Each code shows its official IAB meaning plus a plain-language likely cause and fix
Color-coded category badges make it easy to scan a whole range like 400 to 411
Copy a ready 'code — meaning' line to paste into a ticket, runbook, or Slack thread
Covers wrapper no-fill (303), media-file (401/403/405), and mezzanine (406/411) cases
Runs entirely in your browser — paste an [ERRORCODE] value with nothing uploaded

How to use the VAST Error Code Lookup

Type the error code you saw in the <Error> ping, for example 303 or 402
Read its official meaning, the category it belongs to, and the likely cause and fix
Use the category chips to browse a whole class of errors at once
Copy the code and meaning to drop straight into your bug report or runbook

Example

Input

Output

Category: Wrapper
Meaning: No ads VAST response after one or more Wrappers
Likely cause: the wrapper chain resolved to an empty (no-fill) VAST response.

Looking up 303 explains a common wrapper no-fill you hit while debugging ad ops.

Common errors & troubleshooting

You see error 303 but the VAST tag itself looks valid. — 303 is a no-ad / no-fill after one or more wrappers — the upstream simply had nothing to serve. Check floor prices, targeting, and demand rather than the XML.
The code in your logs is not in this list, e.g. 1009. — Only 100–901 are standard IAB VAST/VPAID codes. Values outside that range are usually vendor- or SDK-specific — check the documentation for the player or ad server that emitted them.
Error 101 keeps firing on a response you believe is correct. — 101 is schema validation: the XML parses but breaks the VAST XSD. Validate the document against the schema for the exact version in the <VAST version> attribute.
You get 403 on an MP4 URL that plays fine in a browser. — 403 means no offered MediaFile matched the player's supported type, codec, or delivery method — not that the file is missing. Add a progressive H.264/AAC MP4 rendition.

Frequently asked questions

What does VAST error code 303 mean?: 303 is a wrapper error: 'No ads VAST response after one or more Wrappers'. The redirect chain resolved to an empty VAST document — a no-fill. The XML is valid; the upstream simply had no ad to serve, so look at demand and targeting, not the markup.
Where do VAST error codes actually come from?: The player substitutes the numeric code into the [ERRORCODE] macro of the ad's <Error> URI and fires it as a tracking pixel. The codes and their meanings are defined in the IAB Tech Lab VAST 3.0 and 4.x specifications.
What is the difference between VAST error 100 and 101?: 100 is an XML parsing error — the response is not well-formed, so it will not parse at all. 101 is schema validation — the XML parses but does not match the VAST schema, for example a missing required element or a misplaced attribute.
Does this cover VPAID error codes as well as VAST?: Yes. 901 is the general VPAID error, alongside the full VAST set. VPAID is deprecated in favour of SIMID and OMID, but 901 still appears when a legacy interactive creative fails to initialise or run.
Why is my error code missing from the lookup?: Only codes 100 through 901 are part of the standard IAB VAST/VPAID range. Codes outside it are typically custom to a specific SDK, player, or ad server, so their meaning lives in that vendor's own documentation.
Can I look up a code without exposing my ad tag?: Yes. The complete code table is bundled into this page, so typing a number or pasting an [ERRORCODE] value is matched locally on your device. No VAST response, ad tag, or error string is sent to ArrayKit.

Related tools

VAST Validator — Validate VAST 2.0-4.3 ad XML against IAB rules and see errors and warnings, in your browser.
VAST Tag Inspector — Inspect a VAST tag as a readable tree of creatives, media files and tracking events.
VAST Macro Expander — Browse VAST 4.x macros and expand a tracking URL with sample or custom values.
VMAP Validator — Validate VMAP ad-break XML and see the ad-break timeline, in your browser.
OpenRTB Enum Reference — Search OpenRTB objects and enums like devicetype, api, protocols and plcmt.
IAB Ad Size Reference — Look up IAB standard ad unit sizes by name or dimensions, like 300x250 and 728x90.