What are the limitations of description and title tags in Yahoo?

Ok, so what's the matter? ;)

Here are the basic guidelines common to all.
The title is the important tag. Others can be used, but search engines deny their use. However, I can see that Google shows the "description" of meta in the search results page for some websites in the result. Why only some do not know me.

Do not overload / overload the tag. Keep the number of words in the title at around 6-8, or better 4-5.
If you add your domain to the title, add it to the end, not the beginning, especially if it does not contain your main keywords.

Keep the meta at about 10-15 words. A small sentence readable by the man.

Use 5 to 6 keywords in the keyword tag and try to keep them separate. Avoid repetition.
Make sure all these keywords are also present on the web page in the article.

And here is a tool I've created that shows how a search engine can see the "spread" of your keywords on the webpage.
Enter a URL and enter 2-3 keywords such as: mobile phone
This will show you how Google sees the spread of these two keywords on the web page.
Check out some of the websites that rank at the top for the same keyword. You will see common patterns coming up.