I need a free tool for webmasters

Tell me a free tool. So that I could check the traffic on my site, find errors, check the speed of loading pages and so on.
I can recommend a tool that I use myself https://senlix.com/ With it, you can perform the following types of checks:
- site traffic;
- check the speed of the site;
- error detection;
- parameters of the CEO;
- analysis and optimization of the site.
All of these features are free.