The method of verifying HTML files mainly includes four steps. 1. Use the official W3C verification tool or third-party website to upload files or enter URLs to get error reports; 2. Install plug-ins in editors such as VS Code and Atom to achieve real-time verification during writing; 3. Pay attention to common problems such as unclosed tags, unquoted attribute values, error nesting, and the use of discarded tags; 4. Automatic verification is achieved through command-line tools such as html-validate or vnu.jar, and integrate it into the construction process to improve team collaboration efficiency.
Verifying an HTML file is actually not complicated, but many people tend to ignore some details. Directly speaking, the purpose of verifying HTML is to ensure that the code complies with standard specifications, so that the web page will perform more consistently in different browsers and be easier to maintain.

1. Use the online HTML verification tool
The easiest way is to use the official verification service provided by W3C, which is the W3C Markup Validation Service . You just need to upload the HTML file or enter the URL, and it will automatically check and list errors or warnings.
- Support local file upload and remote URL checking
- Show which line is wrong and give a brief description
- Friendly to beginners and suitable for quick troubleshooting
In addition to W3C, there are also some third-party websites that can also be used, such as HTML Validator or CSS Lint, but their functions may not be as comprehensive as the official one.

2. Check in real time in the editor
If you usually use VS Code, Sublime Text or other modern code editors, you can install plug-ins to achieve real-time HTML verification. For example:
- VS Code : Install "HTMLHint" or "IntelliSense for CSS class names in HTML"
- Atom : There are plugins similar to linter-htmlhint
The advantage of these plugins is that you can see where there is a problem when writing the code, and you don’t need to upload it manually to verify it every time. After setting up, a syntax error will be automatically prompted when saving the file.

3. Pay attention to common HTML verification errors
Even if you use tools, some errors are likely to occur repeatedly, such as:
- The tag is not closed, such as
<p></p>
No - The attribute value is not quoted, like
class=my-class
- Use tags incorrectly, such as nested in
<p></p>
- Used a discarded tag, such as
<center></center>
or<font></font>
Although these problems will not completely crash the page, they will affect SEO and accessibility and will also increase debugging costs in the long run.
4. Automated verification process (advanced)
If you are working on a project and want to automatically verify HTML during the build process, you can use command line tools such as
html-validate
orvnu.jar
(W3C's local validator). In conjunction with the npm script or CI/CD process, problems can be found before the code is submitted.For example, if you use
html-validate
, you can run it like this:npx html-validate index.html
Rules can also be configured, such as whether self-closing tags are allowed, whether alt attributes are mandatory, etc., which are suitable for team collaboration and standardized development.
Basically these are the methods. Verifying HTML is not difficult, the key is to develop habits, especially if you check it before multiple people cooperate or go online, which can save a lot of trouble.
- Used a discarded tag, such as
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