Company
About RowSlice
RowSlice is a free set of browser-based CSV tools for files too big for Excel: split, merge, remove duplicates and convert to UTF-8, with files processed on your own computer and never uploaded.
It is a small, independent site, launched in September 2026, for one specific problem: CSV files that are too large, too messy or too sensitive for the usual ways of handling them.
Why It Exists
Data exports keep getting bigger, while the everyday tools for handling them have not changed. Excel stops at 1,048,576 rows and quietly changes values like ZIP codes and long IDs. A tool that works by upload sends your file to someone else's server, which a workplace's data rules may not allow, and a tool that loads the whole file into the browser's memory slows down or fails as the file grows. Splitting an export by region or combining a folder of reports should not require writing code.
How the Tools Work
When you choose a file, it is opened by JavaScript running in your own browser tab. The file is read a few megabytes at a time and split into rows and columns following the CSV standard (RFC 4180), and results are written to your browser's private storage on your own disk. When you download the result, it is copied from there to your downloads folder. No part of your file is sent to RowSlice or anyone else.
Because of this, memory use stays low however large the file is. Removing duplicates is the one exception: it keeps a short fingerprint of every different row (or every different value in the columns you compare) it has seen, up to about 33 million of them, and stops with a message beyond that. What limits file size is your free disk space and the storage your browser allows a site, which is about 10 GB in Firefox. Running in the browser also means the tools keep working if you disconnect from the internet after the page has loaded.
How the Tools Are Tested
The tools are tested in the current versions of Chrome, Edge and Firefox on Windows. Safari, and browsers on a Mac, have not been tested, so we make no claim about them. In Firefox, a 1 GB file with 25 million rows was split with every row intact.
Many of the guides are written from runs on test files: in Excel 2021 on Windows 11, and with the commands and scripts shown in the guides. Those guides say which results were measured in those runs and which come from the software makers' own documentation, such as Microsoft's.
Principles
- Correctness first. Rows are copied as text, never reinterpreted, so values come out as they went in.
- No upload, no account. Every tool is free to use without signing up.
- Plain explanations. Every tool page explains what it does to your data and what its limits are.
Contact
Found a file the tools handle incorrectly, or need a CSV job they don't do yet? Email hello@rowslice.com. Please don't attach confidential data; a few made-up rows that show the problem are usually enough.