Creative · IAB Tech Labv0.9.1

VASTlint

Validates, inspects, and repairs VAST ad tags, including wrapper chains, SIMID, VMAP, and DAAST.

What actually goes wrong

A wrapper chain that redirects five hops deep and dies on an HTTP media file renders as a blank slot. The player reports nothing useful and the impression is already gone.

What it does about it

Walk the whole chain, get a stable rule id and a fix for every finding, and auto-repair the deterministic ones.

Findings are structured, not prose. Every one carries a stable rule id you can suppress, track, or cite in a ticket, a severity, the exact location in the payload, and guidance on the fix. The same verdict comes back whether you called the CLI, the library, the browser build, or the MCP server.

Published research
VAST XML Validation at Bid-Time Scale: Latency Analysis and Integration Patterns for Programmatic Video Pipelines

Preprint, ResearchGate, April 2026. A 17 KB CTV tag validates in 350 microseconds, 0.35% of a 100 ms bid window; a 44 KB tag in 2.1 ms, inside a typical creative-selection budget.

Coverage

  • Rule catalog. 132 VAST, 29 DAAST, 25 VMAP, 9 SIMID
  • Rule provenance. Every rule cites its source: the VAST spec, the XSD, an RFC, an ISO list, or a documented revenue impact
  • Beyond validation. Wrapper chain resolution, OMID verification checks, VPAID detection, and deterministic auto-fix
  • Reach. Eleven distribution channels across six language ecosystems

Calling it from an agent

VASTlint exposes 14 tools over the Model Context Protocol, hosted over HTTP with no install and no account. See the MCP overview for wiring it into Claude Code, Cursor, or your own agent loop.

validate_vastvalidate_vast_urlfix_vastlist_rulesexplain_ruleget_adcp_capabilitieslist_content_standardscreate_content_standardsget_content_standardsupdate_content_standardsdelete_content_standardslist_creativescalibrate_contentvalidate_content_delivery

Use it without installing anything

VASTlint runs in the browser at vastlint.org, against the same engine as the CLI. No account and no key.

VAST validator Paste a tag, get every finding with a line number and a fix. No account.Live tag tester Give it a VAST URL and it fetches, validates, and previews the response.Wrapper chain inspector Follow a redirect chain hop by hop to find which one actually breaks.Rule catalog All 195 rules with XML examples, severities, and the spec citation behind each.Platform guides What players, SDKs, DSPs, and CTV platforms actually require.MCP setup Wire the hosted server into Claude, Cursor, or your own agent loop.AdCP explainer How the Ad Context Protocol connects to VAST and creative governance.

Where it fits

VASTlint grades one crossing in the delivery chain. The other two cover the crossings on either side of it: RTBlint and Pixellint. Same output contract, same license, so a team can adopt one and add the others without relearning anything.