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 Firebase is
JSON shaped for a Realtime Database import: an object keyed by record id rather than an array.
Firebase projects.
What changes when you convert Excel to Firebase
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.
Keys come from the first column. Firebase does not store arrays natively, so a keyed object is the correct shape for an import.
What carries over from Excel to Firebase
Excel records 3 things about a table that Firebase has no way to hold.
An empty cell and a missing one are the same thing in Firebase, so a null and an empty string in the Excel both come out blank and can no longer be told apart.
Firebase 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 Firebase and is dropped. The values are what survives.
Both formats record types, so numbers, booleans and nulls survive as themselves rather than as text.