The Nu Html Checker (v.Nu)

The Nu Html Checker (v.Nu) helps you catch unintended mistakes in your HTML, CSS, and SVG. It enables you to batch-check documents from the command line and from other scripts/apps, and to deploy your own instance of the checker as a service (like validator.w3.org/nu). Its source code is available, as are instructions on how to build, test, and run the code.

A Dockerfile (see Pulling the Docker image below) and npm, pip, and brew packages are also available.

It is released upstream in these formats:

• pre-compiled Linux, Windows, and macOS binaries that include an embedded Java runtime
• vnu.jar — a portable version you can use on any system that has Java 11 or above installed
• vnu.war — for deploying the checker service through a servlet container such as Tomcat

Note: The vnu.jar and vnu.war files require you to have Java 11 or above installed. The pre-compiled Linux, Windows, and macOS binaries don’t require you to have any version of Java already installed at all.

You can get the latest release or run docker run -it --rm -p 8888:8888 ghcr.io/validator/validator:latest, npm install vnu-jar, npm install --registry=https://npm.pkg.github.com @validator/vnu-jar, brew install vnu, or pip install html5validator and see the Usage and Web-based checking sections below. Or automate your document checking with a frontend such as:

• Grunt plugin for HTML validation or Gulp plugin for HTML validation or Maven plugin for HTML validation
• html5validator pip package (for integration in Travis CI, CircleCI, CodeShip, Jekyll, Pelican, etc.)
• LMVTFY: Let Me Validate That For You (auto-check JSFiddle/JSBin, etc., links in GitHub issue comments)