What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What YAML is
YAML uses indentation instead of brackets. It is a superset of JSON, supports comments, and is meant to be edited by hand.
Kubernetes manifests, CI pipelines, Ansible playbooks and most modern config files.
What changes when you convert Excel to YAML
Only the first sheet is read, and cells are read as the text Excel displays rather than the number underneath. That matters for dates: a cell showing 15/03/2026 arrives as that string, not as a serial number you would then have to decode.
You get a list of maps, one per row, with long lines left unwrapped so values do not get folded across lines.
What carries over from Excel to YAML
Excel records 2 things about a table that YAML has no way to hold.
YAML has no header row. The column names are repeated as keys on every record instead, which is why the result is bigger on disk than the table it came from.
Anything visual in the Excel - weight, alignment, colour, column widths - has no counterpart in YAML and is dropped. The values are what survives.
Both formats record types, so numbers, booleans and nulls survive as themselves rather than as text.