Everything here is engine-agnostic by design. If you finish this list, you have already covered most of what any crawler can check, and you have removed the differences that usually cause a page to win in one engine and disappear in another.
One query per page. State it in the title and the H1 without padding or slogan.
Answer in the first screen. The definition or conclusion appears before any persuasion.
Serve text in the HTML. Content that needs a script to appear is a risk on every crawler.
One canonical per topic. Parameter and duplicate URLs split signals everywhere.
Descriptive internal links. Anchor text tells every engine what the target page is about.
Fast, stable layout. Core page experience is checked by all major engines now.
Structured data. Mark the service, the organisation and the questions you answer.
Submit the sitemap. Once per engine console, then keep it accurate as pages change.
Correct language tags. Region and language declarations stop engines guessing.
Consistent local data. Same name, address and category everywhere it appears.
Real citations. Mentions from sites the engine already trusts, not bulk directories.
Measure by source. Segment organic traffic per engine before you change strategy.