# VastLint

> **TL;DR.** VastLint is an open-source linter for VAST (Video Ad Serving Template) XML — the IAB standard that delivers video ads to web, mobile, and CTV players.

- **Category:** Developer Tools / Linters / Ad Tech
- **Stage:** validating
- **Age:** 57 days
- **Origin date:** 2026-04-20
- **First detected:** 2026-04-20
- **Canonical URL:** https://earlyterms.com/term/vastlint
- **Sources:** 8 primary URLs

## Definition

VastLint is an open-source linter for VAST (Video Ad Serving Template) XML — the IAB standard that delivers video ads to web, mobile, and CTV players. It validates tags against 108 rules spanning VAST 2.0 through 4.3, surfacing missing fields, malformed URLs, and spec violations as inline squiggles inside the editor.

Built by [Aleksander Sekowski](https://github.com/aleksUIX/vastlint) with a first GitHub push on April 3 and a [Show HN](https://news.ycombinator.com/item?id=47829489) launch on April 20, 2026, VastLint ships one 108-rule Rust engine compiled to WebAssembly and fans out to a [VS Code extension](https://marketplace.visualstudio.com/items?itemName=aleksUIX.vastlint), Open VSX (Cursor, Windsurf, Kiro), a Homebrew CLI, a REST API, Go and JS bindings, plus an MCP server for AI agents — all Apache 2.0, local-first, no paywall.

## Example

A trafficker writes a VAST 4.1 wrapper in VS Code. VastLint flags VAST-2.0-mediafile-https (HTTP MediaFile on an HTTPS page), VAST-4.1-vpaid-apiframework (deprecated VPAID), and a duplicate Impression URL — all before the tag hits QA or a partner ad server.

## Analogy

ESLint for the 200-page IAB video-ad spec — squiggles on broken tags as you type, not three weeks later in a discrepancy report.

## Why it's emerging now

VAST has been the IAB standard for 20 years and carries ~$30B of US video ad spend, but broken tags still get caught in QA or three weeks later in discrepancy reports. VastLint is the first open-source, IDE-native linter covering all 108 rules from VAST 2.0 to 4.3, shipped April 20 to VS Code, Cursor, Windsurf, and Kiro.

## Related terms

- *parent:* VAST (Video Ad Serving Template)
- *parent:* IAB Tech Lab
- *related:* SIMID
- *related:* OM SDK
- *related:* Prebid.js
- *competitor:* htmlhint
- *related:* stylelint
- *related:* kiro
- *related:* agents-md
- *related:* mcp-server

## Sources

1. [Show HN — Vastlint, inline linting for ad tags](https://news.ycombinator.com/item?id=47829489)
2. [DEV Community — I Built a VS Code Extension That Validates VAST XML as You Type](https://dev.to/aleksuix/i-built-a-vs-code-extension-that-validates-vast-xml-as-you-type-2ln)
3. [GitHub — aleksUIX/vastlint](https://github.com/aleksUIX/vastlint)
4. [GitHub — aleksUIX/vastlint-go](https://github.com/aleksUIX/vastlint-go)
5. [vastlint.org — free VAST XML validator](https://vastlint.org/)
6. [Visual Studio Marketplace — vastlint](https://marketplace.visualstudio.com/items?itemName=aleksUIX.vastlint)
7. [Open VSX — vastlint (Cursor/Windsurf/Kiro)](https://open-vsx.org/extension/aleksUIX/vastlint)
8. [IAB Tech Lab — VAST 4.3 spec](https://iabtechlab.com/standards/vast/)

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_Generated by EarlyTerms · https://earlyterms.com/term/vastlint_