CSS HTML Validator (previously named CSE HTML Validator) is an

HTML editor An HTML editor is a program used for editing HTML, the markup of a web page. Although the HTML markup in a web page can be controlled with any text editor, specialized HTML editors can offer convenience, added functionality, and organisation. Fo ...

and CSS editor for

Microsoft Windows Windows is a Product lining, product line of Proprietary software, proprietary graphical user interface, graphical operating systems developed and marketed by Microsoft. It is grouped into families and subfamilies that cater to particular sec ...

(and

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

and other

Unix-like A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...

operating systems when used with

Wine Wine is an alcoholic drink made from Fermentation in winemaking, fermented fruit. Yeast in winemaking, Yeast consumes the sugar in the fruit and converts it to ethanol and carbon dioxide, releasing heat in the process. Wine is most often made f ...

) that helps web developers create syntactically correct and accessible

HTML Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets ( ...

HTML5 HTML5 (Hypertext Markup Language 5) is a markup language used for structuring and presenting hypertext documents on the World Wide Web. It was the fifth and final major HTML version that is now a retired World Wide Web Consortium (W3C) recommend ...

XHTML Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated. While HTML, pr ...

, and CSS documents by locating errors, potential problems like browser compatibility issues, and common mistakes. It is also able to check links, check spelling, suggest improvements, alert developers to deprecated, obsolete, or proprietary tags, attributes, and CSS properties, and find issues that can affect

search engine optimization Search engine optimization (SEO) is the process of improving the quality and quantity of Web traffic, website traffic to a website or a web page from web search engine, search engines. SEO targets unpaid search traffic (usually referred to as ...

. CSS HTML Validator is developed, marketed, and sold by AI Internet Solutions LLC located in

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

. The first version of CSS HTML Validator was released in 1997 for

Windows 95 Windows 95 is a consumer-oriented operating system developed by Microsoft and the first of its Windows 9x family of operating systems, released to manufacturing on July 14, 1995, and generally to retail on August 24, 1995. Windows 95 merged ...

. The current version is 2025/v25.01 (as of January 24, 2025) and is for

Windows 10 Windows 10 is a major release of Microsoft's Windows NT operating system. The successor to Windows 8.1, it was Software release cycle#Release to manufacturing (RTM), released to manufacturing on July 15, 2015, and later to retail on July 2 ...

and above, including

Windows 11 Windows 11 is a version of Microsoft's Windows NT operating system, released on October 5, 2021, as the successor to Windows 10 (2015). It is available as a free upgrade for devices running Windows 10 that meet the #System requirements, Windo ...

. A native

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

and

command line version (called htmlval) became available with version 23. There are currently three main editions of CSS HTML Validator — Pro/Professional, Home/Standard, and Lite. The Enterprise edition was discontinued in 2025/v25. While the application is generally a commercial product (except for the Lite edition), a free version of the Home edition is available for personal/educational, non-commercial use. A free limited version of the htmlval command line tool for macOS and Linux is also available.

Features

CSS HTML Validator includes an

validator A validator is a computer program used to check the Validity (logic), validity or syntactical correctness of a fragment of code or document. The term is commonly used in the context of validating HTML,Tittel, Ed, and Mary C. Burmeister. HTML 4 f ...

for

htmx htmx (also stylized as HTMX) is an open-source front-end JavaScript library that extends HTML with custom attributes that enable the use of AJAX directly in HTML and with a hypermedia-driven approach. These attributes allow for the dynamic d ...

polyglot markup In computing, a polyglot is a computer program or script (or other file) written in a valid form of multiple programming languages or file formats. The name was coined by analogy to multilingualism. A polyglot file is composed by combining synt ...

, CSS,

PHP PHP is a general-purpose scripting language geared towards web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by the PHP Group. ...

and

JavaScript JavaScript (), often abbreviated as JS, is a programming language and core technology of the World Wide Web, alongside HTML and CSS. Ninety-nine percent of websites use JavaScript on the client side for webpage behavior. Web browsers have ...

(using

JSLint JSLint is a static code analysis tool used in software development for checking if JavaScript source code complies with coding rules. It is provided primarily as a browser-based web application accessible through the domain jslint.com, but there ...

or JSHint), link checker (to find dead and broken links),

spell checker In software, a spell checker (or spelling checker or spell check) is a software feature that checks for misspellings in a text. Spell-checking features are often embedded in software or services, such as a word processor, email client, electronic ...

, accessibility checker, and

(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 custom scripting language called TNPL, included in the Pro and Enterprise editions, can be used to customize validations by adding, eliminating, or changing validator messages. TNPL can also be used to integrate customized validation checks to meet the unique requirements of an individual or entity. A Batch Wizard tool, included in the Pro and Enterprise editions, can check entire Web sites, parts of Web sites, or a list of local web documents. The Batch Wizard generates reports in standard HTML or XML format. The reports can be viewed using a normal web browser. The accessibility checker includes support for

Section 508 Amendment to the Rehabilitation Act of 1973 In 1998, the U.S. Congress amended the Rehabilitation Act to require federal agencies to make their electronic and information technology accessible to people with disabilities. Section 508 was enacted to eliminate barriers in information techn ...

and

Web Content Accessibility Guidelines The Web Content Accessibility Guidelines (WCAG) are part of a series published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C), the main international standards organization for the Internet. They are a set of re ...

(both WCAG 1.0 and WCAG 2.0/2.1/2.2). Using a version of

HTML Tidy HTML Tidy is a console application for correcting invalid HyperText Markup Language (HTML), detecting potential web accessibility errors, and for improving the layout and indent style of the resulting markup. It is also a cross-platform library ...

with HTML5 support and the Pretty Print & Fix Tool, CSS HTML Validator can automatically fix some common problems with

and

documents. However, some problems cannot be fixed (or fixed correctly) with automated tools and require manual review and repair.

Version history

Validation of

was added in version 12, and mobile development support (for HTML and CSS) was added in version 14 and improved in version 15. Version 15 added built-in syntax checking for

JSON JSON (JavaScript Object Notation, pronounced or ) is an open standard file format and electronic data interchange, data interchange format that uses Human-readable medium and data, human-readable text to store and transmit data objects consi ...

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

. 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 Google Chrome is a web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macOS, iOS, iPadOS, an ...

CSS HTML Validator 2018/v18 renames the software from CSE HTML Validator to CSS HTML Validator 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 Windows Vista is a major release of the Windows NT operating system developed by Microsoft. It was the direct successor to Windows XP, released five years earlier, which was then the longest time span between successive releases of Microsoft W ...

and below. CSS HTML Validator 2019/v19 includes updated HTML and CSS support, adds WCAG 2.1 support, improves support when running under

Wine (software) Wine is a free and open-source compatibility layer to allow application software and computer games developed for Microsoft Windows to run on Unix-like operating systems. Developers can compile Windows applications against WineLib to help po ...

, and is a native 64-bit application (previously releases were 32-bit). CSS HTML Validator 2020/v20, first released in January 2020, includes HTML, CSS, accessibility, and other updates, including improved support for the Accelerated Mobile Pages Project. Also, beginning with version 20, the Standard edition was renamed to the Home edition. CSS HTML Validator 2021/v21, first released in January 2021, includes further HTML, CSS, accessibility, and other updates. CSS HTML Validator 2022/v22, released in January 2022, includes improvements and updates to keep the program up-to-date, a new Microsoft Edge WebView2 rendering engine for the integrated web browser, and three new dark themes. Later updates to version 22 added support for checking JSON Lines and

NDJSON JSON streaming comprises communications protocols to delimit JSON objects built upon lower-level stream-oriented protocols (such as TCP), that ensures individual JSON objects are recognized, when the server and clients use the same one (e.g. impl ...

documents. CSS HTML Validator 2023/v23, released in January 2023, includes more improvements and updates to keep the program up-to-date. The new release also introduced new command line

and

ports of the core validation engine, called htmlval for Mac and Linux. Official support for Windows 7, 8, and 8.1 was dropped in the 2023/v23 version. CSS HTML Validator 2024/v24, released in January 2024, includes updates and improvements. It also adds support for

. CSS HTML Validator 2025/v25, released in December 2024 and still the current major release, includes further updates and improvements for 2025. Version 25 discontinues the Enterprise edition, moving Enterprise functionality to the Pro 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.

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: * be more accessible for people with

disabilities Disability is the experience of any condition that makes it more difficult for a person to do certain activities or have equitable access within a given society. Disabilities may be cognitive, developmental, intellectual, mental, physica ...

(such as blindness), as well as all users in general * render faster (user agents don't have to "figure out" and decipher bad syntax) * render as intended and with fewer problems on a variety of user agents, including

mobile device A mobile device or handheld device is a computer small enough to hold and operate in hand. Mobile devices are typically battery-powered and possess a flat-panel display and one or more built-in input devices, such as a touchscreen or keypad. ...

s * cause browsers and user agents to build a more consistent

Document Object Model The Document Object Model (DOM) is a cros s-platform and language-independent API that treats an HTML or XML document as a tree structure wherein each node is an object representing a part of the document. The DOM represents a document with ...

, 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 * cause fewer problems for visitors and

web indexing Web indexing, or Internet indexing, comprises methods for indexing the contents of a website or of the Internet as a whole. Individual websites or intranets may use a back-of-the-book index, while search engines usually use keywords and Metadata ( ...

* not contain dead, broken, or rotting links While automated checking tools are helpful for website development and continued maintenance, they cannot guarantee that a document will display (render) and behave 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.

Differences from other HTML validators

* CSS HTML Validator is an offline desktop app for

and a native

and

command line tool that does not require an Internet connection. The offline nature of CSS HTML Validator is in contrast to online web-based services. * CSS HTML Validator primarily works offline (except for link checking when it must go online), which has speed and privacy benefits compared to web-based solutions and services like the

W3C Markup Validation Service The Markup Validation Service is a validator by the World Wide Web Consortium (W3C) that allows Internet users to check pre-HTML5 HTML and XHTML documents for Well-formed element, well-formed markup against a document type definition (DTD). Marku ...

. However, the user must keep the software updated unlike web-based solutions which are typically kept updated by the solution provider. * CSS HTML Validator checks HTML/XHTML syntax, CSS, links, spelling, accessibility,

, SEO, and

with one pass, while DTD-based validators are more limited and cannot check

. * 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.

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 EmEditor is a lightweight extensible commercial text editor for Microsoft Windows. It was developed by Yutaka Emura of Emurasoft, Inc. It includes full Unicode support, 32-bit and 64-bit builds, syntax highlighting, find and replace with regular e ...

- includes a special Lite edition build of CSS HTML Validator for built-in checking of HTML and CSS * Blumentals Software - several Blumentals software products integrate with CSS HTML Validator * HTML-Kit * HomeSite * Microsys A1 Website AnalyzerA1 Website Analyzer
Retrieved 2017-08-11 * TextPad

References

External links

*
Installing CSS HTML Validator on Linux using Wine
{{HTML editors Web development