What an ATS actually does
It takes your file, extracts the text, and tries to work out which part is your name, which is an employer, which is a date range. Recruiters then search that database. If parsing fails, your record is incomplete or garbled — that is the real failure mode, not a rejection algorithm.
This reframes the whole problem. You are not trying to beat a filter. You are trying to be machine-readable.
What breaks parsing
Layout, almost always. Anything that makes the text hard to read in a straight line is a risk.
- Contact details inside a header or footer, which some parsers never read
- Text inside images, including a name rendered as a logo
- Multi-column layouts, which can interleave into nonsense
- Tables used for layout rather than data
- Unusual section names — "Where I've Been" instead of "Experience"
- Dates written inconsistently between entries
What doesn't matter as much as people claim
Keyword density is the big one. Stuffing a skills section with every term from the posting does not raise a score, because there usually is no score — and a human reads the page immediately afterwards.
Fonts, colour, and a tasteful accent are fine. So is a sidebar, provided the underlying text order still makes sense when read linearly. The test is not "does it look plain" but "does the text extract cleanly".
Do use the words in the posting
Not as stuffing — as accuracy. If the posting says "incident response" and you wrote "on-call", a recruiter searching the database for the former will not find you. Use the vocabulary of the industry you're applying into, where it honestly describes what you did.
The honest constraint matters. A term on your resume is a term you can be asked about.
Send a PDF unless told otherwise
Modern systems parse PDFs fine, and a PDF is the only way to guarantee the recruiter sees the layout you designed. Send .docx only when the application explicitly asks for it.
One caveat: the PDF has to contain real text. A scan or an exported image looks identical on screen and extracts as nothing at all.