HTML Inspector

Rust HTML validator focused on runtime risk (DOM correctness + interaction stability), not strict spec conformance.

MSRV: Rust 1.93 (Edition 2024).

• VNU test suite inputs: tests/
• VNU manifest (fixtures metadata): tests/manifest.jsonl (regenerate with python3 scripts/generate_vnu_manifest.py)
• CSS validation backend: css_inspector (crates.io dependency)

Install

From crates.io:

cargo install html_inspector_cli

From a git checkout:

cargo install --path crates/html_inspector_cli

Project goal

Project goal: prioritize validation findings by severity, so the highest severity is reserved for issues that are likely to break real-world behavior as opposed to being strictly spec compliant.

This project is written in Rust to integrate easily with the existing Rust ecosystem.

Severity model

• error: high probability of incorrect behavior (DOM tree corruption, broken interactive semantics, duplicate/conflicting IDs, ARIA that contradicts native semantics)
• warning: works today but brittle (recoverable invalid HTML, deprecated markup, non-fatal a11y issues)
• info: signal/noise (framework-generated markers, minor spec purism)

The CLI defaults to --min-severity warning (errors + warnings). Use --min-severity info to include everything.

Run

Validate a single file:

cargo run -p html_inspector_cli -- file path/to/doc.html

Validate and only report errors:

cargo run -p html_inspector_cli -- --min-severity error file path/to/doc.html

Validate HTML and also check CSS in <style> and style="":

cargo run -p html_inspector_cli -- file path/to/doc.html --also-check-css

Validate a CSS file (delegates to the Rust CSS validator port):

cargo run -p html_inspector_cli -- css path/to/styles.css

Auto-detect by extension/URI:

cargo run -p html_inspector_cli -- check path/or/uri

Run as an HTTP server (vnu-client-style POST-body requests; supports out=json|gnu, level=error|warning, parser=html|xml, and doc=):

cargo run -p html_inspector_cli -- serve 3090 --bind 127.0.0.1

The server also serves a small browser UI at / for validating and comparing results against a running Java vnu checker:

• UI: http://127.0.0.1:3090/
• API (Rust): POST /?out=json|gnu&parser=html|xml&level=error|warning&doc=name
• API (UI helper): POST /api/rust and POST /api/compare

For a more complete CLI command reference, see crates/html_inspector_cli/README.md.

Coverage

Generate Rust test coverage (requires cargo-llvm-cov):

./scripts/coverage.sh

Prior work

This project builds on prior work by W3C Nu Validator: https://github.com/validator/validator