There are three ways to verify that there are errors in the HTML document. 1. Use the W3C Markup Validation Service online tool to upload files, enter URLs or paste code to check syntax and tag issues; 2. Install HTMLHint plug-in in VS Code to achieve real-time detection, timely discover and correct errors; 3. Use the command line tool vnu.jar to batch check multiple files, support local operation and can be integrated into the build process, and can discover syntax and semantic problems. These three methods are applicable to different scenarios, which helps to improve web page compatibility and accessibility.
Verifying an HTML document for errors is not complicated, but it is very important to the compatibility and accessibility of web pages. The most straightforward way is to use some ready-made tools to check whether the code meets the standards.

Use the online verification tool
The most common practice is to use the official verification service provided by W3C - W3C Markup Validation Service . You just need to upload the HTML file, enter the URL or paste the code directly, and it will help you find syntax errors, tag closure problems, etc.

for example:
- The tag is not closed (such as
<p>文本</p>
does not)
- The attribute value is not quoted (such as
class=my-class
) - Used outdated or unsupported tags (such as
<center></center>
)
This type of problem may also be displayed in the browser, but different browsers handle differently, which can easily lead to display exceptions.

Real-time check in the editor
If you want to avoid errors while writing code, you can install the corresponding plug-in in the code editor, such as "HTMLHint" or "IntelliSense for CSS, HTML and JavaScript" in VS Code. They can prompt when you write code and correct them in advance.
The setup method is also very simple:
- Open VS Code
- Install HTMLHint plugin
- Open an HTML file and you can see the error mark
This method is suitable for the development stage, can detect problems in a timely manner and reduce the time for post-debugging.
Batch check using command line tools
If you have multiple HTML files that need verification, you can use command line tools such as vnu.jar
(Nu Html Checker). It can run locally, supports batch detection, and is also convenient for integration into the build process.
Basic operation steps:
- Install Java environment
- Download
vnu.jar
- Run in terminal:
java -jar vnu.jar yourfile.html
This not only allows you to check the syntax, but also find some semantic problems, such as unreasonable structure or lack of accessibility.
Ending
In general, HTML verification is to help you check errors through tools, and the sooner you discover, the easier it is. Quick checking with online tools, assisting coding with editors, or batch processing with command lines are all practical methods. Basically all that. Don’t look at it as simple as it is, it can really avoid a lot of trouble if you do it.
The above is the detailed content of How to validate an HTML document for errors. For more information, please follow other related articles on the PHP Chinese website!

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