Why We Built an Updated VAST Validator for the IAB Standard

Short answer

We built vastlint because the market needs an updated VAST validator and tester for the IAB standard: one that covers more of the modern workflow than the current public baseline, explains what failed, and can run inside browsers, CI, servers, and agent pipelines.

This is not an official IAB Tech Lab product, not a rebrand of the IAB VAST Tag Validator, and not a claim of affiliation. It is an independent validator built against the published IAB Tech Lab VAST specifications, schemas, and related public materials.

What we mean by next-generation

For us, next-generation does not mean replacing the standards owner. It means extending the public validation workflow so a team can move from live tag URL, to wrapper-chain inspection, to resolved XML validation, to fix guidance, to automation without switching mental models every step of the way.

The official IAB Tech Lab validator and tester still matter. They are the standards-owner baseline and an important point of reference. But many production teams now need a wider operational surface: newer-version handling, explicit wrapper workflows, reusable APIs, and tooling that works outside a single browser session.

Where the official IAB tools still matter most

• Official status: they come from the standards owner, which matters for trust, internal sign-off, and standards-baseline checks.
• Reference value: they are the cleanest answer when a team asks for the standards body's own public validator or tester.
• Quick baseline use: they remain useful when you want an official first pass before you get into platform-specific or automation-heavy workflows.
• Ecosystem signaling: if you need the IAB Tech Lab standards hub, validator, tester, or adoption program, those should be linked directly rather than paraphrased through a third party.

Where vastlint goes wider on the public surface

• Version coverage: VASTlint validates VAST 2.0 through 4.3 and documents how the newer end of the standard is handled.
• Workflow coverage: it separates live URL testing, wrapper inspection, and resolved XML validation instead of forcing those jobs into one page.
• Rule transparency: it publishes rule references, methodology, and fix guidance so teams can understand why a tag failed instead of only seeing pass or fail.
• Automation: it runs as a web tool, CLI, npm package, Rust library, Go binding, and MCP endpoint for agent-based ad workflows.
• Operational debugging: it is designed for ad ops, CTV, SSAI, and platform troubleshooting, not only one-off browser checks.

The honest comparison

The right framing is not official versus unofficial, winner takes all. The right framing is what problem are you solving right now. If you need the standards owner's public baseline, use the IAB Tech Lab tools. If you need a broader day-to-day validation and testing workflow for modern VAST operations, start with vastlint and cross-check with the official tools when that baseline matters.

That is also why we avoid claiming that VASTlint is the IAB validator. It is not. A better description is that VASTlint is an updated validator and tester for the IAB VAST standard: independent, broader in workflow, and built for current implementation reality.

What we are explicitly not claiming

• We are not claiming IAB Tech Lab affiliation, endorsement, sponsorship, or trademark ownership.
• We are not claiming that passing VASTlint is the same thing as certification by the standards owner.
• We are not claiming that spec compliance alone guarantees playback in every SDK, player, DSP, SSP, or CTV environment.
• We are not claiming to replace platform-specific checks such as Google IMA, Roku RAF, or ad-server-specific QA.

Why build it anyway

Because modern teams need more than a point-in-time validator page. They need to inspect live tags, trace wrappers, validate the resolved XML, understand the exact failing rule, and then move the same logic into release gates, supply-path QA, and AI-assisted trafficking workflows.

That is the gap vastlint tries to close. It builds on top of the published IAB Tech Lab VAST standard and related public materials, while adding the wider workflow that production ad-tech teams now need.