Validating web pages and contents like HTML, JavaScript, and CSS are important for web sites and application owners. As they are popular technologies they have a lot of different implementations where they can be a bit different from the standard. W3C provides a validator to check and provide feedback about the given web page.
What is W3C (World Wide Web Consortium)?
World Wide Web Consortium (W3C) is an international community where its members, staff try to drive Web standards forward. The main standard W3C working is HTML which is created by Tim Berners-Lee. As a standardizing entity, W3C provides standards and tools to set and check HTML. W3C provides HTML, JavaScrip and CSS validator for web pages.
W3C Validator
The W3C Markup Validator is provided from the Markup Validation Service page. We can see that the W3C Markup Validation service provides some options about delivering web pages and the validation configuration.

Validation Delivery Ways/Methods
From the screenshot, we can see that a web page can be delivered in 3 different ways.
Validate By URI/URL
Validate by URI
will accept the URI or URL of the web page on the internet. Then we will click to the Check
button. This delivery method is also the default and most popular way. In this example, we will check the www.poftut.com web page which is Poftut’s home page.

Validate By File Upload
We can also deliver the web page from the local system by uploading it to the Markup Validation Service. We will select the Validate by File Upload
and then click to the check. Keep in mind that some Internet Explorer versions may not work with this method.

Validate By Direct Input
We can also provide the Markup Code (HTML, JavaScript, CSS) directly to the text editor of the Markup Validation Service. We will use Validate by Direct Input
like below.

HTML/Markup Validation Options
We have learned the methods to validate HTML/Markup. But there are some options that can be used during validation. We can list these options by clicking to the More Options
like below.

Character Encoding
will be detected automatically by default but alternatively, we can select from the list explicitly.Document Type
will be detected automatically by default but we can select from the list lie HTML 1.0, XHTML, etc.List Messages Sequentially
will list error/warning findings in an ordered list manner according to the finding location.Group Error Messages by Type
will group error/warning findings according to the type.Show Source
will list the source code.Show Outline
Clean up Markup with HTML-Tidy
Validate error pages
will validate the event an error page is returned.Verbose Output
will provide a more detailed output.

Benefits Of Validating Site According To W3C
Help Improve Rankings In Search Engines Like Google, Bing, Yandex
Search Engines use a different metric in order to rank between web sites and web pages. One metric is the HTML/JavaScript/CSS validity of the page it ranks. If the Markup (HTML/JavaScript/CSS) has fewer errors or error-free it will rank the given web page higher and better. So validating web pages and sites for markup will provide some hints and ways for higher ranking in search engines like Google, Bing, Yandex.
Help Learning Best Practices
Standards are defined also according to the best practices for the given area. HTML standards are also defined with best practices and updated according to these best practices over time. We can better learn the best practices by testing existing pages or creating some HTML code and validating against these HTML standards and best practices.
Improve Website Visitor Experience
Standards are also defined as making the user experience better. In the end, every visitor or user will benefit from a valid web site and web page with a better experience. With valid web sites and pages, the visitor will see everything perfectly, smoothly as expected by the web site/page owner.
Make Website Browser Friendly
Well in the previous part we have talked about the user’s experience. The web site or page is shown to the visitor by a browser. There are different browsers the users and visitors are using. The markup code (HTML, JavaScript, CSS) will be interpreted and displayed by these browsers. Browsers also try to implement markup standards strictly in general. Making our web site/page will make the web site/page browser friendly.
Multiple Device (Tablet, Phone, Embedded) Accessibility
Today a lot of different types of end-user devices exist. These devices generally have different features, screen sizes, capabilities where it may create some incompatibilities. A validated web site/page will be shown in these different types of devices properly.
Alternative Validators
As the W3C is the markup standard creator for languages like HTML, JavaScript, CSS, etc. it provides the most proper markup validator. But there are alternative markup validators to the W3C version which can provide some extra features. Here are some of them.
Dr. Watson
Dr. Watson is a program error debugger for Windows operating system but is provides some markup validation capabilities which is used with the following validator.

Analyze HTML syntax
Verify regular links
Verify image links
Generate word counts
Spell-check non-HTML text
Compute estimated download speeds
check search engine compatibility
Check site link popularity
HTML Validator (Firefox Plugin)
HTML Validator
is a Firefox plugin where it can only use with Mozilla Firefox browsers. It can be installed from the following link.
https://addons.mozilla.org/en-US/firefox/addon/html-validator/

Firebug
Firebug is another popular plugin used by web developers as a browser plugin. Firebug can also validate HTML, CSS, DOM, JavaScript, and provides detailed error and warnings about validated page. Firebug can be installed from the following links.

CSS HTML Validator
CSS HTML validator is a Windows application which check the HTML, CSS, SEO, accessibility, links, and more on a web page and web site. It is paid applications that have Trial, Standard, Professional, and Enterprise Editions.

Total Validator
Total validator is free and paid web site checker about the HTML, CSS, broken links, spelling errors. It is a cross-platform application where it can work on Windows, Linux, and MacOSX without a problem.
