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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 the Pulling from Docker Hub section below) and npm, pip, and brew packages of it are also available, and it’s released upstream in these formats:

Note: The vnu.jar and vnu.war files require you to have Java 8 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 validator/validator:latest, npm install 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:

Usage

Run the checker with one of the following invocations:
vnu-runtime-image/bin/vnu OPTIONS FILES (Linux or macOS)
vnu-runtime-image\bin\vnu.bat OPTIONS FILES (Windows)
java -jar ~/vnu.jar OPTIONS FILES (any system with Java8+ installed)

…where FILES are the documents to check, and OPTIONS are zero or more of the following options:

--errors-only --Werror --exit-zero-always
--asciiquotes --user-agent USER_AGENT --no-langdetect
--no-stream --filterfile FILENAME --filterpattern PATTERN
--css --skip-non-css --also-check-css
--svg --skip-non-svg --also-check-svg
--html --skip-non-html --format gnu|xml|json|text
--help --verbose --version

The Options section below provides details on each option, and the rest of this section provides some specific examples.

Note: Throughout these examples, replace ~/vnu.jar with the actual path to that jar file on your system, and replace vnu-runtime-image/bin/vnu and vnu-runtime-image\bin\vnu.bat with the actual path to the vnu or vnu.bat program on your system — or if you add the vnu-runtime-image/bin or vnu-runtime-image\bin directory your system PATH environment variable, you can invoke the checker with just vnu.

To check one or more documents from the command line:

  vnu-runtime-image/bin/vnu      FILE.html FILE2.html FILE3.HTML...
  vnu-runtime-image\bin\vnu.bat  FILE.html FILE2.html FILE3.HTML...
  java -jar ~/vnu.jar            FILE.html FILE2.html FILE3.HTML...

Note: If you get a StackOverflowError error when invoking the checker, try adjusting the thread stack size by providing the -Xss option to java:

  java -Xss512k -jar ~/vnu.jar ...
  vnu-runtime-image/bin/java -Xss512k \
      -m vnu/nu.validator.client.SimpleCommandLineValidator ...

To check all documents in a particular directory DIRECTORY_PATH as HTML:

  java -jar ~/vnu.jar            DIRECTORY_PATH
  vnu-runtime-image/bin/vnu      DIRECTORY_PATH
  vnu-runtime-image\bin\vnu.bat  DIRECTORY_PATH

More examples

Note: The examples in this section assume you have the vnu-runtime-image/bin or vnu-runtime-image\bin directory in your system PATH environment variable. If you’re using the jar file instead, replace vnu in the examples with java -jar ~/vnu.jar.

To check all documents in a particular directory DIRECTORY_PATH as HTML, but skip any documents whose names don’t end with the extensions .html, .htm, .xhtml, or .xht:

  vnu --skip-non-html DIRECTORY_PATH

To check all documents in a particular directory as CSS:

  vnu --css DIRECTORY_PATH

To check all documents in a particular directory as CSS, but skip any documents whose names don’t end with the extension .css:

  vnu --skip-non-css DIRECTORY_PATH

To check all documents in a particular directory, with documents whose names end in the extension .css being checked as CSS, and all other documents being checked as HTML:

  vnu --also-check-css DIRECTORY_PATH

To check all documents in a particular directory as SVG:

  vnu --svg DIRECTORY_PATH

To check all documents in a particular directory as SVG, but skip any documents whose names don’t end with the extension .svg:

  vnu --skip-non-svg DIRECTORY_PATH

To check all documents in a particular directory, with documents whose names end in the extension .svg being checked as SVG, and all other documents being checked as HTML:

  vnu --also-check-svg DIRECTORY_PATH

To check a Web document:

  vnu URL

  example: vnu http://example.com/foo

To check standard input:

  vnu -

  example:
echo '<!doctype html><title>...' | vnu -
echo '<!doctype html><title>...' | java -jar ~/vnu.jar -

Options

When used from the command line as described in this section, the checker provides the following options:

--asciiquotes

Specifies whether ASCII quotation marks are substituted for Unicode
smart quotation marks in messages.

default: [unset; Unicode smart quotation marks are used in messages]

--errors-only

Specifies that only error-level messages and non-document-error messages
are reported (so that warnings and info messages are not reported).

default: [unset; all messages reported, including warnings & info messages]

--Werror

Makes the checker exit non-zero if any warnings are encountered (even if
there are no errors).

default: [unset; checker exits zero if only warnings are encountered]

--exit-zero-always

Makes the checker exit zero even if errors are reported for any documents.

default: [unset; checker exits 1 if errors are reported for any documents]

--filterfile FILENAME

Specifies a filename. Each line of the file contains either a regular
expression or starts with "#" to indicate the line is a comment. Any error
message or warning message that matches a regular expression in the file is
filtered out (dropped/suppressed).

default: [unset; checker does no message filtering]

--filterpattern REGEXP

Specifies a regular expression. Any error message or warning message that
matches the regular expression is filtered out (dropped/suppressed).

As with all other checker options, this option may only be
specified once. So to filter multiple error messages or warning messages,
you must provide a single regular expression that will match all the
messages. The typical way to do that for regular expressions is to OR
multiple patterns together using the "|" character.

default: [unset; checker does no message filtering]

--format format

Specifies the output format for reporting the results.

default: "gnu"

possible values: "gnu", "xml", "json", "text" [see information at URL below]

https://github.com/validator/validator/wiki/Service-%C2%BB-Common-params#out

--help

Shows detailed usage information.

--skip-non-css

Check documents as CSS but skip documents that don’t have *.css extensions.

default: [unset; all documents found are checked]

--css

Force all documents to be checked as CSS, regardless of extension.

default: [unset]

--skip-non-svg

Check documents as SVG but skip documents that don’t have *.svg extensions.

default: [unset; all documents found are checked]

--svg

Force all documents to be checked as SVG, regardless of extension.

default: [unset]

--skip-non-html

Skip documents that don’t have *.html, *.htm, *.xhtml, or *.xht extensions.

default: [unset; all documents found are checked, regardless of extension]

--html

Forces any *.xhtml or *.xht documents to be parsed using the HTML parser.

default: [unset; XML parser is used for *.xhtml and *.xht documents]

--also-check-css

Check CSS documents (in addition to checking HTML documents).

default: [unset; no documents are checked as CSS]

--also-check-svg

Check SVG documents (in addition to checking HTML documents).

default: [unset; no documents are checked as SVG]

--user-agent USER_AGENT

Specifies the value of the User-Agent request header to send when
checking HTTPS/HTTP URLs.

default: "Validator.nu/LV"

--no-langdetect

Disables language detection, so that documents are not checked for missing
or mislabeled html[lang] attributes.

default: [unset; language detection & html[lang] checking are performed]

--no-stream

Forces all documents to be be parsed in buffered mode instead of streaming
mode (causes some parse errors to be treated as non-fatal document errors
instead of as fatal document errors).

default: [unset; non-streamable parse errors cause fatal document errors]

--verbose

Specifies "verbose" output. (Currently this just means that the names of
files being checked are written to stdout.)

default: [unset; output is not verbose]

--version

Shows the checker version number.

Web-based checking

The Nu Html Checker — along with being usable as a standalone command-line client — can be run as an HTTP service, similar to checker.html5.org, html5.validator.nu, and validator.w3.org/nu, for browser-based checking of HTML documents over the Web. To that end, the checker is released as several separate packages:

All deployments expose a REST API that enables checking of HTML documents from other clients, not just web browsers. And the Linux, Windows, and macOS binaries and vnu.jar package also include a simple HTTP client that enables you to either send documents to a locally-running instance of the checker HTTP service — for fast command-line checking — or to any remote instance of the checker HTTP service running anywhere on the Web.

The latest releases of the Linux, Windows, and macOS binaries and vnu.jar and vnu.war packages are available from the validator project at github. The following are detailed instructions on using them.

Note: Throughout these instructions, replace ~/vnu.jar with the actual path to that jar file on your system, and replace vnu-runtime-image/bin/java and vnu-runtime-image\bin\java.exe with the actual path to the checker java or java.exe program on your system — or if you add the vnu-runtime-image/bin or vnu-runtime-image\bin directory your system PATH environment variable, you can invoke the checker with just java nu.validator.servlet.Main 8888.

Standalone web server

To run the checker as a standalone service (using a built-in Jetty server), open a new terminal window and invoke the checker like this:

java -cp ~/vnu.jar              nu.validator.servlet.Main 8888
vnu-runtime-image/bin/java      nu.validator.servlet.Main 8888
vnu-runtime-image\bin\java.exe  nu.validator.servlet.Main 8888

Then open http://0.0.0.0:8888 in a browser. (To listen on a different port, replace 8888 with the port number.)

Warning: Future checker releases will bind by default to the address 127.0.0.1. Your checker deployment might become unreachable unless you use the nu.validator.servlet.bind-address system property to bind the checker to a different address:

java -cp ~/vnu.jar \
    -Dnu.validator.servlet.bind-address=128.30.52.73 \
    nu.validator.servlet.Main 8888
vnu-runtime-image/bin/java \
    -Dnu.validator.servlet.bind-address=128.30.52.73 \
    nu.validator.servlet.Main 8888
vnu-runtime-image\bin\java.exe  \
    -Dnu.validator.servlet.bind-address=128.30.52.73 \
    nu.validator.servlet.Main 8888

When you open http://0.0.0.0:8888 (or whatever URL corresponds to the nu.validator.servlet.bind-address value you’re using), you’ll see a form similar to validator.w3.org/nu that allows you to enter the URL of an HTML document and have the results for that document displayed in the browser.

Note: If you get a StackOverflowError error when using the checker, try adjusting the thread stack size by providing the -Xss option to java:

  java -Xss512k -cp ~/vnu.jar nu.validator.servlet.Main 8888
  vnu-runtime-image/bin/java -Xss512k -m vnu/nu.validator.servlet.Main 8888

Deployment to servlet container

To run the checker inside of an existing servlet container such as Apache Tomcat you will need to deploy the vnu.war file to that server following its documentation. For example, on Apache Tomcat you could do this using the Manager application or simply by copying the file to the webapps directory (since that is the default appBase setting). Typically you would see a message similar to the following in the catalina.out log file.

May 7, 2014 4:42:04 PM org.apache.catalina.startup.HostConfig deployWAR
INFO: Deploying web application archive /var/lib/tomcat7/webapps/vnu.war

Assuming your servlet container is configured to receive HTTP requests sent to localhost on port 80 and the context root of this application is vnu (often the default behavior is to use the WAR file's filename as the context root unless one is explicitly specified) you should be able to access the application by connecting to http://localhost/vnu/.

Note: You may want to customize the /WEB-INF/web.xml file inside the WAR file (you can use any ZIP-handling program) to modify the servlet filter configuration. For example, if you wanted to disable the inbound-size-limit filter, you could comment out that filter like this:

<!--
  <filter>
      <filter-name>inbound-size-limit-filter</filter-name>
      <filter-class>nu.validator.servlet.InboundSizeLimitFilter</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>inbound-size-limit-filter</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>
-->

HTTP client (for fast command-line checking)

The checker is packaged with an HTTP client you can use from the command line to either send documents to a locally-running instance of the checker HTTP service — for fast command-line checking — or to a remote instance anywhere on the Web.

To check documents locally using the packaged HTTP client, do this:

  1. Start up the checker as a local HTTP service, as described in the Standalone web server section.
  2. Open a new terminal window and invoke the HTTP client like this:
    java -cp ~/vnu.jar nu.validator.client.HttpClient FILE.html...
    
    vnu-runtime-image/bin/java nu.validator.client.HttpClient FILE.html...
    
To send documents to an instance of the checker on the Web, such as html5.validator.nu/, use the nu.validator.client.host and nu.validator.client.port options, like this:
java -cp ~/vnu.jar -Dnu.validator.client.port=80 \
    -Dnu.validator.client.host=html5.validator.nu \
    nu.validator.client.HttpClient FILE.html...
…or like this:
vnu-runtime-image/bin/java -Dnu.validator.client.port=80 \
    -Dnu.validator.client.host=html5.validator.nu \
    nu.validator.client.HttpClient FILE.html...

Other options are documented below.

HTTP client options

When using the packaged HTTP client for sending documents to an instance of the checker HTTP service for checking, you can set Java system properties to control configuration options for the checker behavior.

For example, you can suppress warning-level messages and only show error-level ones by setting the value of the nu.validator.client.level system property to error, like this:

java -Dnu.validator.client.level=error \
       -cp ~/vnu.jar nu.validator.client.HttpClient FILE.html...
…or like this:
vnu-runtime-image/bin/java -Dnu.validator.client.level=error \
       -cp ~/vnu.jar nu.validator.client.HttpClient FILE.html...

Most of the properties listed below map to the common input parameters for the checker service, as documented at github.com/validator/validator/wiki/Service-»-Common-params.

nu.validator.client.host

Specifies the hostname of the checker for the client to connect to.

default: "127.0.0.1"

nu.validator.client.port

Specifies the hostname of the checker for the client to connect to.

default: "8888"

example: java -Dnu.validator.client.port=8080 -jar ~/vnu.jar FILE.html

nu.validator.client.level

Specifies the severity level of messages to report; to
suppress warning-level messages, and only show error-level ones, set
this property to "error".

default: [unset]

possible values: "error"

example: java -Dnu.validator.client.level=error -jar ~/vnu.jar FILE.html

nu.validator.client.parser

Specifies which parser to use.

default: "html"; or, for *.xhtml input files, "xml"

possible values: [see information at URL below]

https://github.com/validator/validator/wiki/Service-%C2%BB-Common-params#parser

nu.validator.client.charset

Specifies the encoding of the input document.

default: [unset]

nu.validator.client.content-type

Specifies the content-type of the input document.

default: "text/html"; or, for *.xhtml files, "application/xhtml+xml"

nu.validator.client.out

Specifies the output format for messages.

default: "gnu"

possible values: [see information at URL below]

https://github.com/validator/validator/wiki/Service-%C2%BB-Common-params#out

nu.validator.client.asciiquotes

Specifies whether ASCII quotation marks are substituted for Unicode
smart quotation marks in messages.

default: "yes"

possible values: "yes" or "no"

HTTP servlet options

nu.validator.servlet.bind-address

Binds the validator service to the specified IP address.

default: 0.0.0.0 [causes the checker to listen on all interfaces]

possible values: The IP address of any network interface

example: -Dnu.validator.servlet.bind-address=127.0.0.1

nu.validator.servlet.connection-timeout

Specifies the connection timeout.

default: 5000

possible values: number of milliseconds

example: -Dnu.validator.servlet.connection-timeout=5000

nu.validator.servlet.socket-timeout

Specifies the socket timeout.

default: 5000

possible values: number of milliseconds

example: -Dnu.validator.servlet.socket-timeout=5000

Pulling from Docker Hub

You can pull the checker from the https://hub.docker.com/r/validator/validator/ repo at Docker Hub.

To pull and run the latest version of the checker:

  docker run -it --rm -p 8888:8888 validator/validator:latest

To pull and run a specific Docker-Hub tag/version of the checker — for example, the 17.11.1 version:

  docker run -it --rm -p 8888:8888 validator/validator:17.11.1

To bind the checker to a specific address (rather than have it listening on all interfaces):

  docker run -it --rm -p 128.30.52.73:8888:8888 validator/validator:latest

To make the checker run with a connection timeout and socket timeout different than the default 5 seconds, use the CONNECTION_TIMEOUT_SECONDS and SOCKET_TIMEOUT_SECONDS environment variables:

  docker run -it --rm \
     -e CONNECTION_TIMEOUT_SECONDS=15 \
     -e SOCKET_TIMEOUT_SECONDS=15 \
     -p 8888:8888 \
     validator/validator

To define a service named vnu for use with docker compose, create a Compose file named docker-compose.yml (for example), with contents such as the following:

  version: '2'
  services:
    vnu:
      image: validator/validator
      ports:
        - "8888:8888"
      network_mode: "host" #so "localhost" refers to the host machine.

Build instructions

Follow the steps below to build, test, and run the checker such that you can open http://0.0.0.0:8888/ in a Web browser to use the checker Web UI.

  1. Make sure you have git, python, and JDK 8 or above installed.
  2. Set the JAVA_HOME environment variable:
    export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64    <-- Ubuntu, etc.
    export JAVA_HOME=$(/usr/libexec/java_home)            <-- MacOS
  3. Create a working directory:
    git clone https://github.com/validator/validator.git
  4. Change into your working directory:
    cd validator
  5. Start the checker Python script:
    python ./checker.py all

    The first time you run the checker Python script, you’ll need to be online and the build will need time to download several megabytes of dependencies.

The steps above will build, test, and run the checker such that you can open http://0.0.0.0:8888/ in a Web browser to use the checker Web UI.

Warning: Future checker releases will bind by default to the address 127.0.0.1. Your checker deployment might become unreachable unless you use the --bind-address option to bind the checker to a different address:

python ./checker.py --bind-address=128.30.52.73 all

Use python ./checker.py --help to see command-line options for controlling the behavior of the script, as well as build-target names you can call separately; e.g.: