How ATS Scanners Actually Work (Explained by an Engineer)

A technical look at how Applicant Tracking Systems parse, score, and rank resumes — so you can optimize with intent, not superstition.

Step 1: parsing

ATS extracts text from your file. Complex layouts, tables, or images destroy this step.

Step 2: field mapping

The parser assigns each block to a field: contact, work history, education, skills. Non-standard headings misroute your data.

Step 3: keyword scoring

The system compares your resume text against the job description using either TF-IDF or embedding similarity (modern ATS). More overlap = higher score.

Step 4: ranking

Recruiters see resumes sorted by score. The top 25% typically get a human review.

Practical implications

• Formatting bugs are as fatal as missing keywords.

• Synonyms help with embedding-based ATS but not with legacy keyword matchers — include both when possible.

• A 70+ ATS score is the working threshold at most large companies.