Free Online CSV Tools
CSV Files Too Big or Too Broken for Excel
Look inside a file nothing will open, count its rows and columns, find the rows an import will reject, then split it, cut it down to the rows you need, merge it with others or convert it to UTF-8. Everything runs in your browser, so your data never leaves your computer.
- Files too big for Excel
- Never uploaded
- Free, no sign-up
Understand
See What Is Inside the File
Page through a file nothing will open, measure it, see what changed since the last one, and take or make a file to test with.
CSV Analyzer
Count the rows, list the columns and profile the values in a CSV too big to open.
CSV Viewer
Page through and search a CSV that is far too large for Excel, without uploading it.
Compare Two CSV Files
See what was added, removed and changed between two exports, matched on an ID column.
Take a Sample from a CSV
Pull the first rows, every Nth row or a random slice out of a huge file for testing.
Sample CSV File Generator
Download realistic test CSV files from 10 rows up to 20 GB, with messy values on request.
Transform
Cut, Combine and Clean
Make one file into many, many into one, keep only the rows you want, or write it out as Excel or JSON.
Split CSV into Multiple Files
Cut a CSV that Excel refuses to open into multiple files by rows, size or number of parts.
Split CSV by Column Value
One file for every store, region, client or status — straight from a huge export.
Filter CSV Rows
Keep only the rows you need — by value, text match or number range — from a file of any size.
Merge CSV Files
Combine multiple CSV files into one, lining up columns by name, even when the result is too big for Excel.
Remove Duplicates from CSV
Delete repeated rows from millions of records, comparing whole rows or chosen columns.
Convert CSV to Excel
Make a real .xlsx file without losing leading zeros, long IDs or turning codes into dates.
Convert CSV to JSON
Turn a CSV into a JSON array or NDJSON, with every value kept exactly as written.
Convert JSON to CSV
Flatten a JSON array or NDJSON export into a spreadsheet-ready CSV.
Fix
Repair a File That Will Not Import
Find what an import will reject, and put the encoding and delimiter right.
How It Works
Built for the Files Excel Gives Up On
Excel stops at 1,048,576 rows. Anything that has to hold the whole file in memory runs out of room sooner or later, and anything that uploads it makes you wait for the upload and leaves your data on someone else's server. RowSlice is built to get around all three. The CSV limits reference puts that Excel figure beside the published limits of Google Sheets and common import tools, and the ceilings of the tools here, each with its source.
Streams Instead of Loading into Memory
RowSlice reads your file a few megabytes at a time and writes results straight to your disk, so a split, merge or conversion needs no more memory for a huge file than for a small one. What limits size is free disk space and the storage your browser allows a site, about 10 GB in Firefox.
Your Values Stay Exactly as They Are
Rows are copied as text, never interpreted. ZIP codes like 00742 keep their zeros, 16-digit account numbers are not rounded, and product codes are not turned into dates — all things that happen when a CSV passes through Excel.
Private by Design
There is no upload step, no account, and no server that ever sees your data. That makes these tools usable for customer lists, payroll exports, and anything else your company doesn't allow you to put on someone else's website.
Correct with Messy Real-World Files
Quoted values containing commas or line breaks, semicolon- and tab-separated files, Windows-1252 and UTF-16 exports, blank lines and ragged rows are all handled, following the CSV standard (RFC 4180).
Common Problems
Which Tool Fixes My Problem?
| Your problem | What to use |
|---|---|
| You need to look at the rows themselves, and the file is far too big to open in Excel | CSV Viewer pages through it from the first row to the last and searches any column, reading only the part you are looking at. |
| You need to know how many rows are in a file Excel will not open | CSV Analyzer reads the whole file a few megabytes at a time and reports the row count, the columns and what is in each one. |
| Excel says the data set is too large for the grid, or the file was not loaded completely | Split CSV into Multiple Files cuts it into parts of up to 1,000,000 rows that Excel can open, each starting with the header row. |
| You need one file per store, region or client | Split CSV by Column Value writes a separate file for each value in the column you pick, up to 10,000 files. |
| You need the rows for one region or one status, or every order above a figure, and none of the rest | Filter CSV Rows keeps only the rows where the column you pick matches, and writes them to a new CSV with the header. |
| Dozens of monthly exports need to become one file | Merge CSV Files puts every row into one file under a single header row, lining columns up by name. |
| The same customer appears twice | Remove Duplicates from CSV compares whole rows or only the columns you choose, such as email, and keeps the first copy or the last. |
| This week’s export and last week’s look the same, and you need to know what changed | Compare Two CSV Files matches the rows of the two files on an ID column and lists what was added, removed and changed, naming the columns that differ. |
| An import failed and you do not know which rows are wrong | CSV Validator lists the rows an import will reject — wrong number of columns, unclosed quotes, duplicate IDs — with the data row number of each. |
Accents and apostrophes show up as é or ’ | Convert CSV to UTF-8 re-saves the file as UTF-8 with a byte order mark, which tells Excel the file is UTF-8, so accents, apostrophes and other symbols display correctly. |
Opening the CSV in Excel turns 00742 into 742 and SEP-1 into a date | Convert CSV to Excel writes a real .xlsx file with those values already stored as text, so opening it changes nothing. |
| A script or an API wants the data as JSON, not CSV | Convert CSV to JSON writes one JSON array, or one object per line, with every value kept as the text the CSV held. |
| An export arrived as JSON and you need it in a spreadsheet | Convert JSON to CSV turns the objects into rows and their keys into columns, using dotted names like address.city for nested fields. |
| Everything lands in column A | Why your CSV opens in one column in Excel explains the separator mismatch behind it and four ways to fix it. |
| A file is too big to test with, and you need a few thousand rows out of it | Take a Sample from a CSV takes the first rows, every nth row or a random slice, and writes them to a smaller CSV under the same header. |
| You need a big file to test an import | Sample CSV File Generator generates made-up customer, sales order, employee or product records, up to 100 million rows or 20 GB. |
| You need to know whether a file will fit in Excel, Google Sheets or an import tool before you send it | CSV Limits lists the published row, column, cell and size limits of each, with a link to the source of every figure. |
Guides
Guides for Large and Messy CSV Files
- How to Open a CSV File That Is Too Large for ExcelSix ways to work with a CSV that has millions of rows, from free tools to one line of code.
- Excel’s Row Limit: What Happens after Row 1,048,576The exact limits of Excel and Google Sheets, why data goes missing, and how to avoid losing it.
- Stop Excel Removing Leading Zeros from CSV FilesWhy ZIP codes, IDs and phone numbers lose their zeros in Excel, and four ways to keep them.
- Why Your CSV Opens in One Column in ExcelThe delimiter and regional-settings mismatch behind it, and four ways to get proper columns back.
- How to Convert a CSV to Excel without Breaking Your DataOpening a CSV and saving as .xlsx silently changes values. Here is the import route that does not.
- Stop Excel Turning Long Numbers into Scientific NotationWhy card numbers, IMEIs and long IDs get rounded to 15 digits, and how to keep every digit.
FAQ
Questions About These CSV Tools
Do I need to install anything or create an account?
No. Every tool runs as a web page — open it, choose your file, and the work happens in the browser tab you already have. There is nothing to download, no extension, and no sign-up, so nothing about you or your file is stored anywhere.
Which browsers do the tools work in?
Chrome, Edge and Firefox, in their current versions on Windows — those are the three we have tested. Firefox allows a site around 10 GB of disk storage, which was enough to split a 1 GB file with all 25 million rows intact. We have not tested Safari, or any browser on a Mac, so we make no claim about them. No plug-in or extension is needed anywhere.
Are the tools really free, and what is the catch?
They are free to use, with no account, no trial and no paid upgrade. The site shows no advertising today; if it ever does, the ads will be labelled and kept away from the tools themselves. Because your file never reaches a server, a large file costs the site nothing more to handle than a small one, so there is nothing to charge for by size.
Why will Excel not open my CSV file?
Almost always because it has more than 1,048,576 rows, which is the hard limit of an Excel worksheet. Excel loads the first 1,048,576 and warns that not all the data was loaded; everything after that row is missing, and saving at that point writes the truncated version over your data. Six ways to open a CSV that is too large covers what to do instead, why a CSV won’t open in Excel covers the other causes, from locked files to overlong values, and the row, column and cell limits of Excel, Google Sheets and common import tools are listed with their sources.
Will the tools change my values, the way Excel does?
No. Rows are copied through as text and never interpreted, so a ZIP code of 00742 keeps its zeros, a 16-digit account number is not rounded to 15 digits, and a product code like SEP-1 is not turned into a date. Those changes happen when a CSV passes through a spreadsheet, not here.
Can RowSlice open or create Excel (.xlsx) files?
It can create one: Convert CSV to Excel writes a real .xlsx workbook, with leading zeros, long ID numbers and codes like SEP-1 stored as text so that opening the file does not change them. Nothing here reads an .xlsx file, and none of it is a substitute for a spreadsheet when you need to calculate, pivot or chart. Every other tool works in CSV text, and two of them in JSON as well, preparing the file — right size, right delimiter, right encoding — so the import into Excel, Sheets or LibreOffice goes cleanly. See importing a CSV into Excel by hand.
Do the tools keep working without an internet connection?
Yes, once the page has loaded. The code that reads and writes your file is already in the browser at that point, so you can disconnect and finish the job. That also means nothing can be sent anywhere while you work, which is the simplest way to prove a file stayed on your machine.
Analyze, Split and Merge Large CSV Files
Free, no sign-up, and your files are never uploaded.