Both store tabular data. But they're fundamentally different tools for different jobs.
CSV (Comma-Separated Values)
What it is: Plain text. Every row is a line, every column is separated by a comma. That's it. No formatting, no formulas, no charts, no macros.
Use when: Importing/exporting data between systems. Storing data that needs to be version-controlled (Git tracks text changes perfectly). API data exchange. Database imports.
Excel (.xlsx)
What it is: A rich binary format supporting formulas, formatting, charts, pivot tables, macros, multiple sheets, and more.
Use when: You need calculations, visual formatting, or charts. Sharing with non-technical people who expect a 'spreadsheet.' Financial modeling.
Common Gotchas
Excel silently corrupts data: zip codes starting with 0 become numbers (07102 → 7102). Dates get reformatted. Gene names turn into dates (MARCH1 → March 1). If data integrity matters, use CSV and a text editor — not Excel.
Convert between formats easily with our CSV to Excel and Excel to CSV tools.