vastlint

Free Online VAST Tag Validator

Use this free VAST tag validator when you already have the VAST XML and want a pure rule-by-rule compliance check. Drop a .xml file, paste raw XML, or type below. Results appear instantly and nothing is stored.

Need to test a VAST URL, fetch wrappers, or preview the creative? Try the VAST Tag Tester → · Need to debug redirects hop by hop? Open the VAST Inspector →

Drop a .xml file or URL · paste XML or a URL · auto-validates · ⌘↵ to validate now

Full

rule coverage

6

VAST versions

<1ms

validation

0

data stored

WebCLIVS CodeREST APIRustGonpm

How this VAST tag validator works

  • → Validates against IAB VAST 2.0, 3.0, 4.0, 4.1, 4.2, and 4.3 specs. Version is detected automatically from the version attribute.
  • → Checks for missing required fields, malformed URLs, empty elements, deprecated features, VPAID, version mismatches, and more.
  • → Your XML is never stored. The validation response is returned immediately and discarded.
  • → Want validation in CI/CD? Use the vastlint CLI brew install aleksUIX/tap/vastlint
  • → Need a REST API? vastlint is on RapidAPI: validate VAST tags with a single HTTP call. Subscribe free →

VAST tag validator FAQ

What is a VAST tag validator?

A VAST tag validator checks a VAST tag or VAST XML document against the IAB Tech Lab specification. It catches missing required fields, malformed URLs, deprecated elements, and version-specific compliance issues before launch.

How do I validate a VAST tag?

Paste raw XML into the editor, upload a .xml file, or type directly into the validator. If you need live URL fetching, wrapper testing, or creative preview, switch to the VAST Tag Tester.

Which VAST versions are supported?

This VAST tag validator supports VAST 2.0, 3.0, 4.0, 4.1, 4.2, and 4.3. Version detection is automatic from the VAST version attribute.

Keep going

Search visitors who land on the validator usually need one of three things next: a fix guide, a version explainer, an automation path, or a live wrapper-debugging flow. These pages cover the most common follow-up jobs.