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 with clean Problems entries, concise hovers, fix guidance, and direct docs links. Web validator and full documentation: vastlint.org

Features

Inline squiggles — red (error), yellow (warning), blue (info) underlines on the offending XML tag
Hover tooltips — concise issue summary, fix guidance, and a direct rule docs link
Problems panel — clean issue titles with file, line, and column; click to jump directly to the tag
Any file type — works in .xml, .html, .js, .ts, .json, templates — anywhere <VAST> appears
Multi-block — validates every <VAST>...</VAST> block in a file independently
Live as you type — re-validates 500 ms after you stop typing, and on every save
CLI backend — uses the vastlint CLI binary when available, falls back to WASM in-process
121 rules across VAST 2.0–4.3 plus SIMID validation: required fields, schema structure, URLs, deprecations, and CTV/SSAI advisories

How it looks

Hover over a squiggled tag:

🔴 <InLine> is missing required <AdSystem>

✅ Fix: Add `<AdSystem>` inside `<InLine>`, e.g. `<AdSystem>My Ad Server</AdSystem>`.

Docs: vastlint.org/docs/rules/VAST-2.0-inline-adsystem

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 severity overrides (WASM fallback only — use `vastlint.toml` in CLI mode)
`vastlint.templateIgnoreRegex`	`""`	Regex for template expressions to blank out before validation (e.g. `\$\{[^}]+\}`)
`vastlint.vastVersion`	`""`	Force a VAST version (`"2.0"`, `"3.0"`, `"4.0"`, `"4.1"`, `"4.2"`, `"4.3"`) — blank = auto-detect
`vastlint.cliPath`	`"vastlint"`	Path to the `vastlint` CLI binary. Falls back to common install locations, then WASM.

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 121 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)
SIMID interactive creative validation (<InteractiveCreativeFile apiFramework="SIMID">)
Security (HTTP vs HTTPS)
CTV/SSAI best practices (Mezzanine, AdServingId)
Structural issues (wrapper depth, ad sequence, duplicate impressions)

Full rule reference with examples and fix guidance: vastlint.org/docs/rules

Canonical rule catalog:

RULES.md in this repo
vastlint.org/docs/rules for the hosted per-rule pages

All 121 rules

VAST 2.0

Rule	Severity	Description
VAST-2.0-root-element	error	Root element must be `<VAST>`
VAST-2.0-root-version	error	`<VAST>` must have a `version` attribute
VAST-2.0-root-version-value	warning	`version` attribute must be a recognised version string
VAST-2.0-root-has-ad-or-error	error	`<VAST>` must contain at least one `<Ad>` or `<Error>`
VAST-2.0-ad-has-inline-or-wrapper	error	Each `<Ad>` must contain exactly one `<InLine>` or `<Wrapper>`
VAST-2.0-inline-adsystem	error	`<InLine>` must contain `<AdSystem>`
VAST-2.0-inline-adtitle	error	`<InLine>` must contain `<AdTitle>`
VAST-2.0-inline-impression	error	`<InLine>` must contain at least one `<Impression>`
VAST-2.0-inline-creatives	error	`<InLine>` must contain `<Creatives>` with at least one `<Creative>`
VAST-2.0-linear-duration	error	`<Linear>` must contain `<Duration>`
VAST-2.0-linear-mediafiles	error	`<Linear>` must contain `<MediaFiles>` with at least one `<MediaFile>`
VAST-2.0-mediafile-delivery	error	`<MediaFile>` must have a `delivery` attribute
VAST-2.0-mediafile-delivery-enum	error	`delivery` must be `"progressive"` or `"streaming"`
VAST-2.0-mediafile-type	error	`<MediaFile>` must have a `type` attribute
VAST-2.0-mediafile-dimensions	error	`<MediaFile>` must have `width` and `height` attributes
VAST-2.0-mediafile-https	warning	MediaFile URL uses HTTP instead of HTTPS
VAST-2.0-wrapper-adsystem	error	`<Wrapper>` must contain `<AdSystem>`
VAST-2.0-wrapper-impression	error	`<Wrapper>` must contain at least one `<Impression>`
VAST-2.0-wrapper-vastadtaguri	error	`<Wrapper>` must contain `<VASTAdTagURI>`
VAST-2.0-wrapper-depth	error	Wrapper chain depth exceeds the configured maximum
VAST-2.0-companion-resource	error	`<Companion>` must contain at least one resource element
VAST-2.0-companion-dimensions	warning	`<Companion>` missing `width` or `height`
VAST-2.0-nonlinear-resource	error	`<NonLinear>` must contain at least one resource element
VAST-2.0-nonlinear-dimensions	warning	`<NonLinear>` missing `width` or `height`
VAST-2.0-ad-sequence	warning	Inconsistent use of `sequence` attribute across `<Ad>` elements
VAST-2.0-text-only-element	error	Text-only element contains a child element
VAST-2.0-unknown-attribute	warning	Attribute not defined in the VAST spec
VAST-2.0-inline-unknown-child	error	`<InLine>` contains an unrecognised child element
VAST-2.0-wrapper-unknown-child	error	`<Wrapper>` contains an unrecognised child element
VAST-2.0-creatives-unknown-child	error	`<Creatives>` may only contain `<Creative>` elements
VAST-2.0-creative-unknown-child	error	`<Creative>` contains an unrecognised child element
VAST-2.0-linear-unknown-child	error	`<Linear>` contains an unrecognised child element
VAST-2.0-trackingevents-unknown-child	error	`<TrackingEvents>` may only contain `<Tracking>` elements
VAST-2.0-mediafiles-unknown-child	error	`<MediaFiles>` contains an unrecognised child element
VAST-2.0-extensions-unknown-child	error	`<Extensions>` may only contain `<Extension>` elements
VAST-2.0-videoclicks-unknown-child	error	`<VideoClicks>` contains an unrecognised child element
VAST-2.0-nonlinearads-unknown-child	error	`<NonLinearAds>` contains an unrecognised child element
VAST-2.0-nonlinear-unknown-child	error	`<NonLinear>` contains an unrecognised child element
VAST-2.0-companionads-unknown-child	error	`<CompanionAds>` may only contain `<Companion>` elements
VAST-2.0-companion-unknown-child	error	`<Companion>` contains an unrecognised child element
VAST-2.0-creativeextensions-unknown-child	error	`<CreativeExtensions>` may only contain `<CreativeExtension>` elements
VAST-2.0-extension-misplaced-element	warning	`<Extension>` contains an element that has a dedicated location in the VAST spec
VAST-2.0-extension-cdata	warning	`<Extension>` leaf text payload with XML-sensitive characters should be wrapped in CDATA so JSON blobs and URL-rich vendor data do not rely on fragile XML escaping
VAST-2.0-creative-extension-misplaced-element	warning	`<CreativeExtension>` contains an element that has a dedicated location in the VAST spec
VAST-2.0-creative-extension-cdata	warning	`<CreativeExtension>` leaf text payload with XML-sensitive characters should be wrapped in CDATA so JSON blobs and URL-rich vendor data do not rely on fragile XML escaping
VAST-2.0-tracking-https	warning	Tracking or click URL uses HTTP instead of HTTPS
VAST-2.0-url-cdata	warning	URI value is not wrapped in CDATA
VAST-2.0-url-empty	error	URL field is empty
VAST-2.0-url-invalid	warning	URL field does not appear to be a valid URI
VAST-2.0-parse-error	error	XML parse error — document may be malformed
VAST-2.0-version-mismatch	warning	Declared version does not match structural signals
VAST-2.0-duplicate-impression	warning	Duplicate `<Impression>` URL within the same `<Ad>`
VAST-2.0-flash-mediafile	warning	Flash MediaFile type is no longer supported
VAST-2.0-linear-tracking-quartiles	warning	`<Linear>` has no standard quartile tracking events — measurement system receives no signal
VAST-2.0-duration-format	error	Duration value does not match `HH:MM:SS[.mmm]` format

VAST 3.0

Rule	Severity	Description
VAST-3.0-progress-offset	error	`<Tracking event="progress">` requires an `offset` attribute
VAST-3.0-progress-offset-format	warning	Progress `offset` does not match the required format
VAST-3.0-skipoffset-format	warning	`skipoffset` does not match `HH:MM:SS[.mmm]` or `n%` format
VAST-3.0-skip-event-no-skipoffset	warning	`skip` tracking event present but `<Linear>` has no `skipoffset` attribute
VAST-3.0-minmaxbitrate-pair	error	`<MediaFile>` must have both `minBitrate` and `maxBitrate` or neither
VAST-3.0-bitrate-conflict	warning	`<MediaFile>` has both `bitrate` and `minBitrate`/`maxBitrate`
VAST-3.0-icon-attrs	warning	`<Icon>` missing recommended attributes (`program`/`width`/`height`/position)
VAST-3.0-icon-program	error	`<Icon>` missing required `program` attribute
VAST-3.0-icon-width	error	`<Icon>` missing required `width` attribute
VAST-3.0-icon-height	error	`<Icon>` missing required `height` attribute
VAST-3.0-icon-xposition	error	`<Icon>` missing required `xPosition` attribute
VAST-3.0-icon-yposition	error	`<Icon>` missing required `yPosition` attribute
VAST-3.0-icon-resource	error	`<Icon>` must have at least one resource element
VAST-3.0-icons-unknown-child	error	`<Icons>` may only contain `<Icon>` elements
VAST-3.0-icon-unknown-child	error	`<Icon>` contains an unrecognised child element
VAST-3.0-iconclicks-unknown-child	error	`<IconClicks>` contains an unrecognised child element
VAST-3.0-pricing-model	error	`<Pricing>` missing required `model` attribute
VAST-3.0-pricing-currency	error	`<Pricing>` missing required `currency` attribute
VAST-3.0-pricing-model-case	warning	`model` value should be lowercase (`cpm`/`cpc`/`cpe`/`cpv`)
VAST-3.0-pricing-currency-format	warning	`currency` attribute must be a 3-letter ISO 4217 code
VAST-3.0-companion-required-attr	warning	`<CompanionAds>` `required` attribute must be `all`, `any`, or `none`

VAST 4.0

Rule	Severity	Description
VAST-4.0-wrapper-root-error	warning	`<VAST>` root contains both `<Ad>` and `<Error>` elements
VAST-4.0-universaladid-present	error	`<Creative>` must contain `<UniversalAdId>` (VAST 4.0+)
VAST-4.0-universaladid-idregistry	error	`<UniversalAdId>` must have an `idRegistry` attribute
VAST-4.0-universaladid-idvalue	error	`<UniversalAdId>` missing required `idValue` attribute (VAST 4.0)
VAST-4.0-category-authority	error	`<Category>` missing required `authority` attribute
VAST-4.0-companion-clicktracking-id	error	`<CompanionClickTracking>` missing required `id` attribute
VAST-4.0-wrapper-clickthrough	warning	`<ClickThrough>` inside Wrapper `<VideoClicks>` was removed in VAST 4.0
VAST-4.0-conditionalad	warning	`conditionalAd` attribute is deprecated as of VAST 4.1
VAST-4.0-tracking-event-removed	warning	Tracking events removed in VAST 4.0
VAST-4.0-mediafile-apiframework	info	`apiFramework` on `<MediaFile>` is deprecated — use `<InteractiveCreativeFile>`
VAST-4.0-interactive-creative-no-api	warning	`<InteractiveCreativeFile>` should have an `apiFramework` attribute

VAST 4.1

Rule	Severity	Description
VAST-4.1-adservingid-present	error	`<InLine>` must contain `<AdServingId>` (VAST 4.1+)
VAST-4.1-ad-serving-id-empty	warning	`<AdServingId>` is present but empty
VAST-4.1-universaladid-idvalue-removed	warning	`idValue` attribute was removed in VAST 4.1
VAST-4.1-universaladid-content	error	`<UniversalAdId>` must have text content in VAST 4.1+
VAST-4.1-adtype-value	warning	`adType` must be `video`, `audio`, or `hybrid`
VAST-4.1-survey-deprecated	warning	`<Survey>` is deprecated as of VAST 4.1
VAST-4.1-vpaid-apiframework	warning	VPAID is deprecated as of VAST 4.1
VAST-4.1-vpaid-in-interactive-context	warning	VPAID `<MediaFile>` alongside `<InteractiveCreativeFile>` — unsupported in CTV
VAST-4.1-interactive-creative-type	warning	`<InteractiveCreativeFile>` should have a `type` attribute
VAST-4.1-mezzanine-delivery	error	`<Mezzanine>` missing required `delivery` attribute
VAST-4.1-mezzanine-type	error	`<Mezzanine>` missing required `type` attribute
VAST-4.1-mezzanine-width	error	`<Mezzanine>` missing required `width` attribute
VAST-4.1-mezzanine-height	error	`<Mezzanine>` missing required `height` attribute
VAST-4.1-mezzanine-recommended	info	No `<Mezzanine>` present — tag may be rejected in CTV/SSAI contexts
VAST-4.1-verification-vendor	error	`<Verification>` missing required `vendor` attribute
VAST-4.1-verification-no-resource	warning	`<Verification>` should have `<JavaScriptResource>` or `<ExecutableResource>`
VAST-4.1-js-resource-apiframework	error	`<JavaScriptResource>` missing required `apiFramework` attribute
VAST-4.1-exec-resource-apiframework	error	`<ExecutableResource>` missing required `apiFramework` attribute
VAST-4.1-exec-resource-type	error	`<ExecutableResource>` missing required `type` attribute
VAST-4.1-blockedadcategories-no-authority	warning	`<BlockedAdCategories>` should have an `authority` attribute
VAST-4.1-tracking-event-value	error	`event` attribute not in the valid set for this VAST version
VAST-4.1-companion-renderingmode-value	warning	`renderingMode` must be `default`, `end-card`, or `concurrent`

VAST 4.2

Rule	Severity	Description
VAST-4.2-closedcaptionfiles-unknown-child	error	`<ClosedCaptionFiles>` may only contain `<ClosedCaptionFile>` elements
VAST-4.2-icon-fallback-image-width-height	warning	`<IconClickFallbackImage>` should have `width` and `height` attributes

VAST 4.3

Rule	Severity	Description
VAST-4.3-js-resource-browser-optional	warning	`<JavaScriptResource>` should have a `browserOptional` attribute

SIMID rules

Rule	Severity	Description
SIMID-1.0-simid-type-required	error	`<InteractiveCreativeFile apiFramework="SIMID">` must have `type="text/html"`
SIMID-1.0-simid-url-empty	error	`<InteractiveCreativeFile apiFramework="SIMID">` must contain a non-empty URL
SIMID-1.0-simid-url-https	error	`<InteractiveCreativeFile apiFramework="SIMID">` URL must use HTTPS
SIMID-1.0-simid-variable-duration-value	warning	`<InteractiveCreativeFile>` `variableDuration` attribute must be `"true"` when present
SIMID-1.0-simid-mediafile-required	error	Linear SIMID ad must include a video/audio `<MediaFile>` alongside the interactive creative
SIMID-1.1-nonlinear-simid-no-iframe	error	`<NonLinear apiFramework="SIMID">` must contain an `<IFrameResource>`
SIMID-1.1-iframe-simid-type-required	warning	`<IFrameResource>` in SIMID `<NonLinear>` should have `type="text/html"`
SIMID-1.1-iframe-simid-url-empty	error	`<IFrameResource>` in SIMID `<NonLinear>` must contain a non-empty URL
SIMID-1.1-iframe-simid-url-https	error	`<IFrameResource>` in SIMID `<NonLinear>` URL must use HTTPS

Requirements

No external tools needed - the validator runs entirely in-process via WebAssembly.

License

Apache-2.0 - see LICENSE

vastlint — VAST XML Validator

aleksuix