ATS Guide: How Applicant Tracking Systems Actually Work

What an ATS does (and what it doesn't)

Most of what is written about ATS software treats it as a robot judge. The documentation from vendors that publish it describes something more ordinary:

• Collects applications from job posts, career sites and job boards in one place.
• Parses resumes into structured fields (name, contact details, employers, titles, dates, education, skills) and keeps your original file attached to the profile.
• Lets recruiters search and filter candidates, for example by keyword or job title. Greenhouse documents full-text keyword search of resumes (Greenhouse Support).
• Runs the hiring workflow: stages, scorecards, interview scheduling and rejection reasons.
• Applies rules the employer configures. In Greenhouse, auto-reject works on how an applicant answers specific application questions (yes/no, single-select or multi-select), not on resume wording (Greenhouse Support: Auto-reject).

How resume parsing works and where it fails

Parsing means the system reads your file, finds which text is a job title, which is a date, which is a school, and writes it into profile fields. When it can't do that, the file is still attached, but the fields come out empty or wrong. Greenhouse's own support article on unsuccessful parses is the clearest public list of causes, and it matches what most parsers struggle with:

That list comes from one vendor's documentation. Workday, iCIMS, Taleo and others publish less, and behaviour can vary by employer configuration. The overlap is large enough that following the list above is sound advice for any system. We go through what is and isn't publicly documented in Workday vs Greenhouse vs Lever and in our Workday application guide.

Does an ATS score your resume?

There is no universal "ATS score". Parsing success is one thing; ranking or matching candidates against a job is another, and whether it happens depends on the product and on how the employer has set it up. Some systems offer AI-assisted features, some don't; recruiters can also simply search.

That matters for tools like ours. Any "ATS score" a resume checker shows you, Redvica's included, is an estimate of how readable your file is and how well it matches a posting. It is not the number a specific employer's system produced. We explain exactly what our scores are, and aren't, on the methodology page.

PDF or DOCX?

Greenhouse accepts .doc, .docx, .pdf, .rtf and .txt uploads (Greenhouse Support: supported formats), so for that system both main formats are fine. What matters is how the file was made, not the extension (more in PDF or DOCX):

• A text-based PDF (exported from Word, Google Docs or a resume builder) keeps its layout and has selectable text.
• A DOCX is a safe default when the posting asks for Word or doesn't say.
• A scanned or image-only PDF has no text for a parser to read. Test: open the file and try to select a line of text. If you can't, it's an image.
• If the employer names a format, use that one.

An ATS-friendly resume checklist

1. Single column, top to bottom. Keep decorative multi-column layouts for sending directly to a person (we tested this).
2. Plain section headings: Experience, Education, Skills, Projects.
3. Name, email, phone and location in the body at the top, not in the page header.
4. Full job titles and full company names, each with consistent dates (for example "Jan 2024 – Mar 2026").
5. Standard bullet characters and common fonts; no text inside images or text boxes.
6. A Skills section that lists tools and skills as plain words, plus the same terms used in your bullets as evidence.
7. A small file, exported as a text-based PDF or DOCX.
8. No photo or graphics unless the employer or your country's norms expect one, in which case use a version for people, not for upload forms.

Single-column resume templates are the safest option for online applications; the two-column designs are better kept for sending to a person directly. The resume builder offers both. For a longer version of this list, see the ATS-friendly format guide.

Keywords: what actually helps

Recruiters search the way they think: job titles, tools, certifications, domain terms. So your resume should use the same words the posting uses for things you genuinely have done.

• Read the job post and list the skills, tools and requirements it repeats.
• Use those exact terms where they truthfully describe your work, inside real bullets, not only in a keyword dump.
• Spell out an acronym once with the short form, for example "Search Engine Optimization (SEO)", since people search either way.
• Don't claim skills you can't discuss in an interview. A gap belongs in a cover letter or a learning plan, not a fake line.

Our step-by-step keyword method walks through it. Doing this per application is the idea behind job-specific tailoring: it compares your resume with one posting, shows the missing keywords, and only applies the changes you approve.

How to check your own resume

You can do a quick manual check: copy all the text out of your PDF into a plain text editor and read it. If the order is scrambled or details are missing, a parser will likely struggle too. For a faster check, the free Redvica resume checker scans your file for formatting problems, estimates how five well-known systems (Workday, Greenhouse, Lever, iCIMS, Taleo) may handle it, lists missing keywords against a job description, and rewrites weak bullets. The scoring is AI-generated and described on the methodology page.