vastlint — VAST XML Validator for VS Code
Inline linting for IAB VAST ad tags directly in VS Code.
Supports VAST 2.0 through 4.3.
Features
- Inline squiggles — red (error), yellow (warning), blue (info) underlines on the offending XML tag
- Hover tooltips — hover over any squiggle to see the rule ID, what's wrong, and exactly how to fix it
- Problems panel — all issues listed with file, line, and column; click to jump directly to the tag
- Live as you type — re-validates 500ms after you stop typing, and on every save
- Configurable — silence rules, change severities, or set a minimum severity threshold
How it looks
Hover over a squiggled tag:
🔴 vastlint `VAST-2.0-inline-adsystem`
<InLine> is missing required <AdSystem>
✅ Fix: Add `<AdSystem>` inside `<InLine>`, e.g. `<AdSystem>My Ad Server</AdSystem>`.
📖 IAB VAST 2.0 §2.3.1 — `/VAST/Ad[0]/InLine`
Settings
| Setting |
Default |
Description |
vastlint.enable |
true |
Enable/disable diagnostics |
vastlint.minSeverity |
"info" |
Minimum severity to show: "error", "warning", or "info" |
vastlint.ruleOverrides |
{} |
Per-rule overrides, e.g. { "VAST-2.0-mediafile-https": "off" } |
Example: silence HTTP warnings
// .vscode/settings.json
{
"vastlint.ruleOverrides": {
"VAST-2.0-mediafile-https": "off",
"VAST-2.0-tracking-https": "off"
}
}
Example: only show errors
{
"vastlint.minSeverity": "error"
}
Rules
vastlint checks ~80 rules across:
- Required elements and attributes (VAST 2.0–4.3)
- Value formats (durations, URLs, enums)
- Schema conformance (unknown elements/attributes)
- Deprecation warnings (VPAID, Flash, Survey, conditionalAd)
- Security (HTTP vs HTTPS)
- CTV/SSAI best practices (Mezzanine, AdServingId)
- Structural issues (wrapper depth, ad sequence, duplicate impressions)
See the full rule catalog for details.
Requirements
No external tools needed — the validator runs entirely in-process via WebAssembly.
License
Apache-2.0 — see LICENSE
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