How to replace the site with a newer one while maintaining all the url and positions in the search?

Question

Google

Hello, please tell me, there is an old site, it has products, categories, a blog, etc. The site has a good position in the search. Now this site is being updated to a new one, but we keep the domain and url of products, blog articles, categories, pages of various ones. The question is, are there any tools that can be used to check if we have lost any page or any product? I just would like to be sure that after replacing the site with a new one, the pages will not fall out of the search due to the fact that, for example, at some url, there will be 404, and earlier there was a page on the same url on the old site. Or is it just to write a script yourself then that will test it?
Thank you in advance for your response.

Answer 1

Well, a ready-made free tool is Yandex.Webmaster and Google, respectively. It keeps all the statistics on crawling pages, response codes, errors, which specific pages stop working, and so on. Better not to find.
Plus, be sure to log all 404s somewhere after switching on the new design and monitor the first weeks with your eyes just in case.

Answer 2

as an option, do not give the first time 404, but for example 5 **, at the same time log what could not be found there and gradually return it as it was.
but it seems that with a change in layout, the positions will still go down a little