Is it possible for an html code not to work?

I have just wrote a line of html code from the net and it was working but i when i copy and the pastte the code from that site it works.So i thought i have been making mistakes while i tipyng so when i throuhg my code several times, line by line word by word everything is correct but it still not working so i was wondering is it possible to work on code before uploading it ?

There could be various reasons for this problem: some external assets are reachable online but not locally, due to relative paths being used; or the browser you’re using is enforcing some restriction on local HTML pages, for security reasons.

HTML itself is not a programming language, so it’s either well-formed or not, and how malformed HTML docs are handled depends on how tolerant is the browser you’re using. But HTML pages can contain scripts, or include external scripts (from the web, or from the file system).

Most major browsers offer developer tools (e.g. in Chrome use F12 to access the developer tools), which will list all the errors and problems found, and allow you to open the culprit file, and even offer links to guidelines regarding the specific problem. I strongly suggest you learn how to use Chrome developers tools.

So, probably your HTML code is correct, but it’s designed to work online for some reason (e.g. it uses relative paths to assets which are not found on your local machine). The browser developer tools allow to immediately spot these kind of problems, and even test editing the page (or its CSS/JS assets) directly in the browser.