How recruiters actually find you
The mental model most candidates have is a robot reading their resume and scoring it. That is largely a myth. What actually happens is closer to a search engine: your resume is parsed into fields, those fields are indexed, and a recruiter with sixty applications and forty minutes types the two or three skills that matter most into a search box.
You are either in those results or you are not. There is no score, no threshold, and no rejection, just absence. This is why vocabulary matters so much more than it should: the search matches words, and a perfect description of the same work in different words does not match.
Repetition is the signal
Job descriptions are written by people, usually in a hurry, often by pasting from a previous one. The things that genuinely matter get mentioned more than once, in the summary, in the responsibilities, and again in the requirements. The nice-to-haves appear once, in a list.
So a term's repetition count is a decent proxy for how much the hiring manager cares, and this tool surfaces it rather than treating every word as equal. A term marked ×4 is worth restructuring a bullet point for. A term appearing once probably is not.
Tailoring without lying
There is a real line here, and it is worth being clear about which side of it to stand on.
Legitimate: using the employer's vocabulary for work you genuinely did. If you built reporting pipelines and the posting calls it "data engineering", use their term. If you managed relationships with senior internal customers and they call it "stakeholder management", use theirs. You are translating, not inventing.
Not legitimate: adding a skill you do not have because it appeared in the missing list. It will surface in the first technical conversation, and the cost of being caught is far higher than the cost of not matching a keyword.
The honest use of a list of missing terms is as a prompt: for each one, ask whether you have done something that the employer would recognise under that name. Often you have, and simply called it something else.
Do this after the parsing works
Keyword coverage is worth nothing if the resume does not parse. A two-column layout scrambles your text before any search runs against it, and no amount of keyword tuning fixes that.
So run the ATS checker first and clear anything it flags as a blocker. Then come back here and tune the vocabulary against the specific posting. In that order, both steps are worth doing; in the reverse order, the second is wasted.