CSV tools that stay in your browser
Six things people need to do to a CSV, each of them free and each of them running inside the tab. The file is read off your disk by the browser and never sent anywhere. That is the part most online CSV tools get to skip explaining, because they upload it.
Open a CSV file in your browser
Drop a file in. It opens here, and it stays here.
Open itRun SQL on a CSV file
Real SQL, on your file, without installing a database.
Open itMerge CSV files into one
Several files in, one file out, columns matched by name.
Open itRemove duplicate rows from a CSV
Duplicates on the columns you say identify a row.
Open itCompare two CSV files
Added, removed, changed, matched on a key rather than line by line.
Open itConvert a CSV to PDF
A CSV, laid out as a readable table, saved as a PDF.
Open it
What “nothing is uploaded” means here
Your file is opened by the browser and parsed by a database engine running inside the page, so there is no request that carries it anywhere. The engine itself (DuckDB, compiled to WebAssembly) is downloaded from a public CDN the first time you open a file: that is program code arriving, not your data leaving.
Nothing is stored either. There is no account, no database and no recent-files list, so closing the tab is all the clearing up there is. If you want a file to still be there tomorrow, that is what the apps are for.