Google Search Console is Google's free reporting tool for website owners. It shows which searches your site appeared for, how many people clicked, which pages are indexed and which have errors. It is also where Google sends warnings about your site, and the one tool every business owner should have access to in their own name.
It is not an analytics tool. Search Console reports what happened on Google before the click. GA4 reports what happened on your site after it. Owning both, and being able to log in without asking an agency, is the difference between reading a report and being able to check one.
Google Search Console exposes Google's view of a property: Performance (queries, pages, countries, devices, search appearance, sixteen months of data), Page indexing with reasons, URL Inspection (live test and indexed version), sitemaps, Core Web Vitals field data from CrUX, manual actions, security issues and removals. Verify as a Domain property via a DNS TXT record so every protocol and subdomain is covered.
Give the owner Owner-level access on their own Google account and add agencies as Full users so access can be withdrawn. The Search Analytics API returns the same performance data for dashboards. The UI samples and caps rows, the API returns far more per request.
google-site-verification=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (DNS TXT record) 