HTML Validation · Recommended HTML Validation Tools for J1 Template

An HTML validator is a program that checks the formal validity (correctness) of a document for compliance with the W3C HTML standards. For example, a validator checks a document for:

missing necessary elements, e.g. such as <head> and </head>
faulty elements like <span> as a direct child of <ul>
missing attributes such as <alt> on the <img> tag
invalid attributes like <alt> at the <ul> tag
unknown elements or attributes such as <fantasy>
wrong nested elements such as using <h2> before <h1>

The web designer thus receives valuable information on the development of valid websites according to the World Wide Web Consortium (W3C) standards.

The W3C

The W3C (World Wide Web Consortium) is an international community and standards organization that develops and maintains open standards for the World Wide Web. It was founded in 1994 by Tim Berners-Lee, the inventor of the World Wide Web.

The primary mission of the W3C is to ensure the long-term growth and stability of the web by promoting interoperability and fostering the development of open and accessible web technologies. The consortium comprises member organizations, including companies, educational institutions, governmental bodies, and individual participants who contribute to developing web standards.

By developing and promoting web standards, the W3C plays a crucial role in maintaining the integrity and interoperability of the World Wide Web. Its work helps shape the future of web technologies and ensures a consistent and accessible web experience for users worldwide.

W3C Compliance

You should create W3C-compliant websites as much as possible to display your websites correctly. Try to create your source code as validly as possible with your HTML editor and thus adhere to the World Wide Web Consortium (W3C) web standards. The benefits of doing this are obvious:

your internet pages are displayed correctly by different browsers
your web pages will be smaller and load faster.
after some training, your websites can be created and developed more easily.
every web developer can further develop your web pages according to the standards.
Your websites are future-proof and safer.
compliance with the specifications of the W3C consortium improves the search engine rankings of your website (SEO, Search Engine Optimization)

W3C Validator

The W3C Validator, also known as the W3C Markup Validation Service, is a tool provided by the World Wide Web Consortium (W3C) that allows you to check the validity and conformance of web documents against the W3C standards.

The W3C Validator primarily validates HTML (Hypertext Markup Language), CSS (Cascading Style Sheets), and some XML-based document formats. It examines the markup code and checks if it adheres to the syntax and rules specified by the respective W3C standards.

To use the W3C Validator, you must provide the URL or upload the web document file you want to validate. The validator then processes the document, performs the necessary checks, and generates a report highlighting any errors or warnings found.

The report includes detailed information about the issues encountered, line numbers, and suggestions for resolving them. You can easily check the syntax of your code with the W3C Markup Validation Service:

access the W3C's Free HTML and CSS Validator.
enter the URL of the web page to be checked, upload the HTML code as a file, or enter the code directly
click on button Check and you’re done!

As a result of the first test step, you will receive an overview of the HTML and CSS errors found with precise instructions on fixing them. For example, you will find exact line details and error causes in the test result. Typical issues are a forgotten closing tag like </p>, the deprecated use of a CSS statement, or incorrect nesting of tags, e.g., B. Using <h2> before <h1>. The check results allow you to correct your document’s mistakes easily.

In a second test step, you can have your source code edited automatically via More Options and Clean up Markup with HTML-Tidy.

The W3C's Markup Validation Service also supports validating the Document Type Definition (DTD) for HTML. For example, the HTML validator checks that the document has a <head> section and uses the correct HTML skeleton and doctype.

<!DOCTYPE html>
<html>
  <head>
    <title></title>
  </head>
  <body>
  </body>
</html>

Overall, the W3C Validator offers many helpful functions for checking the correct HTML syntax. The validator also supports the development of barrier-free or barrier-free websites. Unfortunately, the testing service does not offer the possibility of validating the source text for different browser versions.

The WHATWG

The WHATWG (Web Hypertext Application Technology Working Group) is a community-driven organization focused on developing and evolving web standards. It was formed in 2004 as a response to perceived stagnation in developing HTML and related web technologies within the W3C (World Wide Web Consortium).

The primary goal of the WHATWG is to maintain and develop specifications for web technologies that are practical, forward-looking, and responsive to the needs of web developers and users. The organization follows an open and consensus-based approach, encouraging active participation from individuals and organizations involved in web development.

In addition to HTML, the WHATWG is involved in developing other web technologies, such as the DOM (Document Object Model) API, web APIs, and related specifications. It focuses on practical implementation details, interoperability, and addressing real-world challenges faced by web developers.

While the WHATWG operates independently of the_W3C_, the two organizations have ongoing collaboration and communication. The WHATWG's work has influenced the development of HTML and related standards within the W3C, leading to a convergence of efforts in some areas.

Nu Html Checker

The Nu Html Checker is an Open Source validator developed by WHATWG (Web Hypertext Application Technology Working Group) for validating HTML documents. It is designed to check the conformance of HTML code against the HTML Living Standard, which is the specification maintained by the WHATWG.

The Nu Html Checker is based on the same underlying engine as the HTML parsing algorithm used in modern web browsers. It provides an accurate and up-to-date analysis of HTML documents, considering the evolving nature of web standards. This validation tool is based on the HTML validator developed by Henri Sivonen. It tests for correctly using HTML, CSS, and graphics in the SVG file format. However, the document type definition (DTD) must be tested here. The Nu Html Checker is open source and is being further developed as a project hosted at Github.

The Nu Html Checker is free for Linux, Windows, and macOS. You can verify a URL, enter an HTML code snippet, or upload a file. The Nu Html Checker complements the W3C Validator and provides an alternative option for validating HTML code. Developers and organizations widely use it to ensure the conformance, quality, and accessibility of their HTML documents, aligning with the latest standards defined by WHATWG.

HTML Validator Alternatives

Two other HTML validators allow you to validate code via file upload or code entry. Both can be used for free as well.

AppDevTools

The HTML Validator at appdevtools.com is also based on the WHATWG's Nu Html Checker. As a special feature, this validator allows validating of only parts of the HTML code. To do this, activate the Fragment option. The HTML code is then treated as part of an HTML document, not a complete one.

The site appdevtools.com provides additional validators for YAML and JSON. The free format HTML validator is based on the W3C's Nu Html Checker. The online tool supports HTML5, SVG 1.1, MathML 3.0, ITS 2.0, and RDFa Lite 1.1.

FreeFormatter

The site freeformatter.com offers additional validators for XML and JSON. The additional tools may perfectly accompany your tests for some other aspects of your code.

The site freeformatter.com provides a rich set of additional tools that are quite helpful for developing a website in general.