An applicant tracking system does two things: it parses your resume into structured data (name, roles, dates, skills), and it ranks you against a specific job description. Any 'ATS checker' that gives you a score without a job description is scoring vibes.
Parsing failures are the #1 reason resumes get rejected silently. Tables, text inside images, headers/footers, multi-column layouts, and unusual fonts all break the parser. If the ATS can't find your job titles, your application is dead before a recruiter opens it.
Keyword matching is real, but not in the way people think. ATS systems don't do exact string matching in most cases — they use taxonomy (they know 'JS' means JavaScript, 'PM' means Product Manager). But they still miss synonyms. Mirror the job posting's exact terms when it costs you nothing.
The checker that matters is one that: (1) parses your resume the way an ATS would, (2) extracts real keywords from a real job posting, and (3) shows you exactly which sections to add them to. Not a score. A diff.
Try DraftlyCV's free ATS checker — paste a job description, upload your resume, get a per-section keyword map in about 15 seconds.