How ATS Works
It is a database with a parser in front of it. The parser is the part that fails people.
Most “ATS rejections” are parsing failures wearing a scarier name.
First it parses
Your file is broken into fields: name, contact, employers, titles, dates, education, skills. This step is mechanical, and it is where most damage happens.
Then it is searched
A recruiter queries that database. You are not scored out of a hundred and rejected — if the parse went wrong, you are simply hard to find.
Then a human decides
Nothing about the shortlist is automatic. The system narrows the pile; a person still chooses. Write for the person, but survive the parser.
Before
Contact details in the document header. Dates written 'Mar 2021', '03/22' and '2023-01'.
After
Contact details in the body, first three lines. Every date as 'Mar 2021'.
Many parsers never read header and footer regions, so the first version can produce a candidate record with no email address at all. Mixed date formats produce broken or missing employment history.
Do this before moving on
Save your resume as plain text and open it. What you see is roughly what the parser sees. If your name, contact details, employers and dates are not all present and in a sensible order, fix that before you touch anything else.
Check yourself
Your resume has your email only in the page header. What is the likely result?