Date First Published: 8th November 2022
Topic: Web Design & Development
Subtopic: Web Applications
Article Type: Computer Terms & Definitions
Difficulty: MediumDifficulty Level: 5/10
Learn more about what a HTML validator is in this article.
A HTML validator is an application used to check that the HTML markup is valid, free of syntax errors and deprecated elements, and follows the standards of the W3C. After performing the checks, the HTML validator will return with a list of errors and warnings. Sometimes, an error in a HTML document can cascade and cause more errors further down the document, making the validator report even more errors. If there are no errors or warnings, the validator will return a success message that may say 'No errors or warnings to show'.
Unlike XML which has strict validation, meaning that any errors in the code will cause the whole file to fail when processed for output, HTML does not have strict validation, meaning that errors in HTML markup will cause the specific element to stop working, but not the entire document and the webpage can still be rendered. The output may just be different than expected, but this can make it harder to spot syntax errors, which is why it is recommended to use a HTML validator to check the validity of HTML markup before publishing a webpage. Examples of syntax errors are missing closing tags, forgotten quotation marks, open elements, etc. A HTML validator can detect all of these syntax errors and specify the line of the error so that website owners can fix them.
Some HTML validators are web-based and don’t require any software to be installed on the user’s computer and others might require a plugin or an application to be installed. Most HTML validators are available free of charge, although some may require a fee.
The W3C Markup Validation Service is an example of a free HTML validator to check the validity of a HTML document. HTML can be checked by direct input, copying and pasting the webpage URL, or uploading a HTML file. There is also a CSS validator to check the validity of CSS files, called Jigsaw. It can be found here. There is also a free HTML validator extension for Google Chrome that can be found on the Chrome Web Store that will check the markup of HTML pages.
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