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W3C
validator.w3.org
The W3C Markup Validation Service
This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, MathML, etc. If you wish to validate specific content such as RSS/Atom feeds or CSS stylesheets, MobileOK content, or to find broken links, there are other validators and tools available.
W3 Nu Html Checker
This tool is an ongoing experiment in better HTML checking, and its behavior remains subject to change · Show sourceoutlineimage reporterrors & warnings onlycheck error pagesUser-Agent Accept-Language
W3C Feed Validation Service, for Atom and RSS
Check the syntax of Atom or RSS feeds · Validate a feed online:
W3 Broken Link Checker
This Link Checker looks for issues in links, anchors and referenced objects in a Web page, CSS style sheet, or recursively on a whole Web site. For best results, it is recommended to first ensure that the documents checked use Valid (X)HTML Markup and CSS.
validator service by the World Wide Web Consortium
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 markup against a document type … Wikipedia
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SitePoint
sitepoint.com › html & css
HTML error finder - HTML & CSS - SitePoint Forums | Web Development & Design Community
April 27, 2012 - Yes, Dw has a built in validator and highlights invalid code in code view. I find this addon for Firefox useful though. ... I can’t argue with the w3.org validator. It is technology-agnostic and singular of purpose. If I might chip in here, I’ve built a validator on top of validator.nu, which is also what the w3 uses. It’s called http://html.validator.pro.
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Nestify
nestify.io › blog › common-html-errors-to-avoid-how-to-check-them
Common HTML Errors to Avoid & How to Check Them
January 14, 2025 - To access them, right-click on your webpage, select “Inspect” or “Inspect Element,” and navigate to the “Console” tab. This section will display any HTML errors, warnings, or issues that the browser encounters when rendering the page.
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FreeFormatter
freeformatter.com › html-validator.html
Free Online HTML Validator - FreeFormatter.com
Validates HTML files for compliance against the W3C standards and performs linting to assess code quality against best practices. Find missing or unbalanced HTML tags in your documents, stray characters, duplicate IDs, missing or invalid attributes and other recommendations.
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Quora
quora.com › How-can-I-find-HTML-errors-on-a-website
How to find HTML errors on a website - Quora
March 9, 2024 - Breaking the HTML elements means ... will save your hours of finding the error and solving it. ... To check for them, use an online validator....
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GeeksforGeeks
geeksforgeeks.org › html › how-to-check-for-errors-in-html
How to check for errors in HTML ? - GeeksforGeeks
October 31, 2021 - In the below example, there are some syntax errors like incomplete p tag, incomplete h1 tag, but still, it displays some of the content in an expected way. In this case, the initial p tag and h1 tag but the next p tag is displayed as h1. These scenarios are easy to identify and avoid in small codes but when the length of code increases, it will be complex to debug code. ... <!DOCTYPE html> <html> <head> <title>HTML errors</title> </head> <body> <h1>HTML errors</h1> <p>unclosed paragraph tag <h1>its displaying the way it is intended <p>but it may lead to next unexpected thing </body> </html>
Find elsewhere
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MDN Web Docs
developer.mozilla.org › en-US › docs › Learn › HTML › Introduction_to_HTML › Debugging_HTML
Debugging HTML - Learn web development | MDN
April 3, 2025 - Later on we will show you how to find errors in HTML using a tool called the HTML validator, but first we will show you how to inspect your HTML manually using a DOM inspector, and then explore what kinds of markup errors you might be looking for, and how the browser might interpret those. All modern browsers have a set of developer tools (devtools) built into them, which provide a set of functionality for examining the webpage loaded into the current tab. These can show you what HTML is rendered in the page, what CSS is applied to each DOM node, what JavaScript is running in the page, and more. They also allow you to edit the currently-running code and see the effect live on the page.
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Quora
quora.com › How-do-you-check-HTML-errors
How to check HTML errors - Quora
Answer (1 of 3): HTML errors are mostly breaking the syntax Example Improper closing tags or double/single quotes Most of the errors in HTML are highlighted by code editor itself.
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Chami
chami.com › html-kit › faq › pages › tidy_introduction.html
How do I check my HTML pages for errors?
January 11, 2026 - Any errors, warnings or suggestions produced by "HTML Tidy" will be displayed in the "Messages Window". To jump to the HTML code related to an error, double click the message.
Top answer
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Visual Studio Code doesn't have HTML validation by default. But it allows you to add extensions and enable these features.

To add HTML validation (linting), open Visual Studio Code, and then press Ctrl + P. Then paste ext install HTMLHint in it, and press Enter. It will install an HTML validator. You may need to reload Visual Studio Code to load the extension.

Now if you open the same HTML document you had the syntax error in, you should see there's an issue shown at the status bar at the bottom :), and it will also show you the errors in those lines.

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Visual Studio Code by default supports code formatting and it tracks the syntactical errors. If you create a new file and directly try to write the code then Visual Studio Code would not be able to understand which language or type of syntax the user wants to format or correct.

So, one first needs to save the new file with the proper extension, and then Visual Studio Code can properly identify the syntax.

The code formatting is available in Visual Studio Code through the following shortcuts:

  • On Windows Shift + Alt + F
  • On Mac Shift + Option + F
  • On Ubuntu Ctrl + Shift + I

You can add Auto Close Tag from the Visual Studio Code marketplace.

Launch Visual Studio Code Quick Open (Ctrl + P), paste the following command, and press Enter.

  1. Automatically add the HTML/XML close tag, the same as Visual Studio IDE or Sublime Text

    ext install auto-close-tag
    
  2. Visual Studio Code integration for HTMLHint - A Static Code Analysis Tool for HTML

    ext install HTMLHint
    
  3. Provides CSS class name completion for the HTML class attribute based on the CSS files in your workspace. It also supports React's className attribute.

    ext install html-css-class-completion
    
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Computer Hope
computerhope.com › issues › ch001274.htm
How to Test and Check a Web Page for Errors
June 1, 2025 - WAVE - Fantastic service for evaluating how accessible a web page is with full details and suggestions on errors and warnings detected. Colorblind filter - See how your page appears to those who have color blindness. Using this page ensures that if someone visiting your site has color blindness, won't miss something because your color scheme is bad. html2txt - A great method of converting your HTML page into a text document.
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BrowserStack
browserstack.com › home › guide › how to debug your html and solve errors?
How to Debug your HTML and solve errors? | BrowserStack
January 14, 2024 - A developer can make mistakes while ... results. Usually, these are common syntax errors because of small typos or closed tags left by the developer. So it’s important to check the HTML codes in a validation tool to find such bugs or errors and resolve them fast...
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CodeBasics
code-basics.com › frontend › html course › errors in html markup
Errors in HTML markup | HTML | CodeBasics
May 22, 2021 - Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.
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LambdaTest
lambdatest.com › home › blog › how to debug html errors and fix them?
How To Debug HTML Errors And Fix Them? | TestMu AI ...
January 29, 2018 - One of the most common issues developers encounter in HTML is syntax errors. Even if you’re experienced, you can still make mistakes when writing lots of HTML code. These errors can cause functions not to work or programs to show the wrong results. They often happen because of small typos or forgotten closed tags. That’s why a validation tool is essential to check your HTML code. It helps you quickly find ...
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LinkedIn
linkedin.com › all › site development
How do you test and validate your HTML code for errors and compatibility?
March 14, 2024 - This tool checks your code against the HTML standards and reports any errors or warnings. You can either enter your URL, upload your file, or paste your code directly into the tool. The tool will highlight the errors and suggest how to fix them.
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Commontools.org
commontools.org › tool › html-validator-78
Free Online HTML Validator Tool | HTML Syntax Checker | HTML Checker | Commontools.org
November 3, 2023 - If your HTML code has errors or warnings, you will see a message indicating the number of errors and warnings found. ... Scroll down to the "Error and Warnings" section. You will find a detailed table that lists the details of each error or ...
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YouTube
youtube.com › watch
How To Error Check (Validate) HTML Code With Nu HTML Checker - YouTube
This is a demo of how the W3C's HTML5 error checker (Validator) works. As of this recording the validator is experimental so don't say I didn't warn you.
Published   September 11, 2015
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JSON Formatter
jsonformatter.org › html-validator
HTML Validator Online to validate HTML data: W3C HTML Validator
Shows errors with line numbers and very easy to correct HTML code. ... Best and Secure Online HTML Validator works well in Windows, Mac, Linux, Chrome, Firefox, Safari and Edge.