1. Features

CSS HTML Validator includes an HTML editor, validator for HTML, XHTML, polyglot markup, CSS, PHP and JavaScript (using JSLint or JSHint), link checker (to find dead and broken links), spell checker, accessibility checker, and search engine optimization (SEO) checker. An integrated web browser allows developers to browse the web while the pages are automatically validated.

Because documents are checked locally and not uploaded over the Internet to a server in order to be checked, validations are performed relatively quickly, and security and privacy are increased.

A Batch Wizard tool, included in some editions of the software, can check entire Web sites, parts of Web sites, or a list of local web documents. The Batch Wizard generates reports in HTML or XML format. The reports can be viewed using a standard web browser.

The accessibility checker includes support for Section 508 Amendment to the Rehabilitation Act of 1973 and Web Content Accessibility Guidelines (both WCAG 1.0 and WCAG 2.0/2.1). Current versions also provide support for Canada's Common Look and Feel (CLF), including CLF 2.0.

Using a version of HTML Tidy with HTML5 support and the Pretty Print & Fix Tool, CSS HTML Validator can automatically fix some common problems with HTML and XHTML documents. However, some problems cannot be fixed (or fixed correctly) with automated tools and require manual review and repair.

2. Version History

Validation of polyglot markup was added in CSE HTML Validator v12, and mobile development support (for HTML and CSS) was added in CSE HTML Validator v14 and improved in v15. Version 15 added built-in syntax checking for JSON and HTML5 cache manifest files. Version 16 added JavaScript linting using JSHint, a static code analysis tool for checking JavaScript, but also continues to support JSLint. Version 17 added support for the Accelerated Mobile Pages Project, which is a type of HTML optimized for mobile web browsing, and support for live DOM validation using Google Chrome^[1]

Version 18 renamed the software to CSS HTML Validator 2018 and includes updated HTML5 and CSS support. Version 18 also added a new "By Message" report in the Batch Wizard and dropped support for Windows Vista and below.

CSS HTML Validator 2019/v19 includes updated HTML and CSS support, adds WCAG 2.1 support, improves support when running under Wine, and is a native 64-bit application (previously releases were 32-bit). CSS HTML Validator 2020/v20, first released in January 2020, includes further HTML, CSS, accessibility, and other updates, including improved support for the Accelerated Mobile Pages Project. Also, beginning with 2020/v20, the standard edition was renamed to the home edition.

An online edition based on CSS HTML Validator Pro that can check documents via file upload, URL, or snippets (direct text input) was discontinued May 2017 in favor of the desktop version for Microsoft Windows.^[2]

3. Purpose of Validation

The purpose of validation and computerized checking of HTML, XHTML, and CSS documents is to help make sure that the documents are syntactically correct and problem-free. Checked HTML, XHTML, and CSS documents are more likely to:

• render faster and with fewer problems (user agents don't have to "figure out" and decipher bad syntax)
• cause browsers and user agents to build a more consistent Document Object Model, which is important for CSS and JavaScript
• be forward-compatible with future versions of user agents and browsers ("future-proof")
• be compatible with current and future HTML, XHTML, and CSS specifications
• render as intended on a variety of user agents, including mobile devices
• cause fewer problems for visitors
• be more accessible for people with disabilities (such as blindness), as well as users in general
• not contain dead, broken, or rotting links

While automated checking tools are helpful for website development and maintenance, they cannot guarantee that a document will display as intended in all browsers. Developers should always test documents in a variety of browsers (including mobile browsers) to locate problems that cannot be detected with a computerized checking tool.

4. Differences from Other HTML Validators

• CSS HTML Validator is an offline desktop app for Microsoft Windows that does not require an Internet connection. The offline nature of the app is in contrast to online services like the W3C Markup Validation Service.
• CSS HTML Validator checks HTML/XHTML syntax, CSS, links, spelling, accessibility, JavaScript, SEO, and PHP with one pass, while DTD-based validators are often more limited, checking mostly for basic tag structure and allowable attributes.
• CSS HTML Validator includes a built-in scripting language (called TNPL) which allows for a high degree of customization via scripting and "user functions". This allows developers to add custom (specialized) validation checks and messages.
• CSS HTML Validator includes a DTD-based validator which can optionally be used for checking DTD-based versions of HTML (versions prior to HTML5), however one of CSS HTML Validator's primary differences is that its custom validation engine can perform more checks on a document than a DTD-based validator can. This is because DTD-based validators are limited to checking only what can be specified in a Document Type Definition.

5. Integration

CSS HTML Validator integrates with other third-party software like those listed below. This allows validation using CSS HTML Validator from within the third-party program.

• EmEditor - includes a special lite edition build of CSS HTML Validator 2019 for built-in checking of HTML and CSS
• Blumentals Software^[3] - several Blumentals software products integrate with CSS HTML Validator
• HTML-Kit
• HomeSite
• Microsys A1 Website Analyzer^[4]
• PhpED^[5]
• TextPad
• TopStyle^[6] - includes link checking support