> you should always explicitly set the canonical URL for each page.
Could someone explain or give a reliable article that explains this well?
Could someone explain or give a reliable article that explains this well?
Theres no way for them to know whether or not the extra params on the URL change the result page. (i.e. example.com/index.php?post_id=1 and example.com/index.php?comment_id=1 could be very different pages, or they could be the same; you don't know).
So in comes the canonical url! This tells Google the proper url required for a specific page. That way if Google gets to a page using two different urls, it can tell that they are the same page.
You can list it by adding a tag to your HTML head.
You can even do face things like rewrite urls entirely (i.e. If the crawler hits example.com/?category_id=1&item_id=2, you can correct the ugly url by listing the canonical url as example.com/category/1/item/2)