How can we identify the errors in html

Question

how can we identify the errors in html

Answer 1

html is a markup language and it's difficult to identify errors in it.
use this website to validate your doc

https://validator.w3.org/
The W3C Markup Validation Service

Answer 2

Some editors shows you some errors, as opening web code in sololearn playground on web site (click on the tiny icons in margin will show details)...

Desktop browsers provide also developers tools which can be helpful for debugging, by exploring the DOM (document object model tree) as it is interpreted by browser parser, so you can look for differences from your source code (and better understand how is working/builded the html structure).

https://developer.mozilla.org/en-US/docs/Tools