VASTlint MCP server

VASTlint

Website & web validator: VAST tag validator Paste a VAST tag and get results in your browser, no install required.

A high-performance VAST XML validator built on a pure-Rust core. Checks ad tags against the IAB Tech Lab VAST specification so you don't have to read it. Over $30 billion in annual CTV and video ad spend flows through VAST XML, and malformed tags are one of the most common causes of lost impressions, broken tracking, and revenue discrepancies between platforms. There is no widely adopted open-source tool that validates VAST XML against the full IAB specification across all published versions.

VASTlint ships a native MCP server - making VAST validation available as a callable tool from Claude, Cursor, the AAMP Buyer Agent SDK, or any MCP-compatible client. Connect to vastlint.org/mcp and call validatevast, validatevasturl, inspectvast, listrules, explainrule, or fix_vast. Each tool returns structured JSON with rule IDs, XPath locations, and spec references.

Native bindings for realtime ad pipelines: vastlint-go (CGo, prebuilt static libs, no Rust toolchain needed), vastlint-java (gRPC client for JVM ad servers), vastlint-erlang (Elixir/Erlang: OTP port mode for production ad delivery, DirtyCpu NIF for non-critical paths), and a WASM npm package for Node.js and browsers. All bindings share the same compiled Rust core. Consistent results everywhere, sub-millisecond latency at scale.

Need a copy-paste frontend starting point? See the React drop-in example in npm/examples.

Validates VAST documents against:

Shortened. The full README is on GitHub.