To download the Java client v2 API jar, you can use the following command:

npm install @openapitools/openapi-generator-cli

Then, run the OpenAPI Generator CLI with the --input option to specify the input file and the --output option to specify the output directory. For example:

openapi-generator-cli generate --input-spec your-openapi-spec.json --output-dir output-directory

This will generate the API client libraries, server stubs, documentation, and configuration for you.

Alternatively, you can use the following command to download the vnu.jar file directly:

npm install vnu-jar

Then, run the Nu Html Checker with the following command:

java -jar vnu.jar your-html-file.html

This will check your HTML file for any Nu Html errors.