What does it actually check?

Roughly thirty things: rows with too many or too few values, garbled characters, blank cells, repeated rows, mixed date formats, numbers stored as text, stray spaces, and inconsistent spellings within a column.

Does it change my file?

No. It only reads and reports. Each problem it finds links to the tool that fixes it, with the settings already filled in, and you decide whether to run it.

Why does it say my dates are ambiguous?

Because 03/04/2026 is the third of April in most of the world and the fourth of March in the United States. When a column could be either, you are asked rather than guessed at.

Can I share the report?

Yes, the report can be saved and sent on. It contains only counts and a few example values, so it is far less sensitive than the file itself.

What if my file is fine?

It says so plainly rather than inventing something to complain about. A clean file is a normal outcome.

Is my file uploaded anywhere?

No. When you check a CSV file for problems here, the work happens inside this page and the browser is told to block outbound connections, so there is no upload to intercept. Watch the Network tab of your developer tools while you check a CSV file for problems: the only requests are for this site’s own code, and none carries your file.

Check a CSV file for problems

Drop a file and see what is wrong with it: blanks, repeated rows, garbled characters, mixed date formats, numbers stored as text. Nothing is uploaded.

Check a file for problemsRunning on your device

Source

Your file

or drag one here · it stays on your device

Result

Add a file. Every check runs on this device, and what it finds appears here.

How this works

Add your file. Drop any spreadsheet onto the page.
Read the report. Each finding shows how many rows are affected and a few examples.
Fix what matters. Follow a finding straight into the tool that fixes it, already configured.

What it cannot do

Inconsistent-spelling detection compares values within a column and will flag genuinely different entries that happen to look alike, so treat it as a prompt to look rather than an instruction to change.
The report reads the whole file twice — once for the checks, once for the column statistics; very large files take proportionally longer, though memory use stays flat.
It reports problems it recognises, so a clean report means nothing known was found rather than that the data is correct.

Questions

What does it actually check?: Roughly thirty things: rows with too many or too few values, garbled characters, blank cells, repeated rows, mixed date formats, numbers stored as text, stray spaces, and inconsistent spellings within a column.
Does it change my file?: No. It only reads and reports. Each problem it finds links to the tool that fixes it, with the settings already filled in, and you decide whether to run it.
Why does it say my dates are ambiguous?: Because 03/04/2026 is the third of April in most of the world and the fourth of March in the United States. When a column could be either, you are asked rather than guessed at.
Can I share the report?: Yes, the report can be saved and sent on. It contains only counts and a few example values, so it is far less sensitive than the file itself.
What if my file is fine?: It says so plainly rather than inventing something to complain about. A clean file is a normal outcome.
Is my file uploaded anywhere?: No. When you check a CSV file for problems here, the work happens inside this page and the browser is told to block outbound connections, so there is no upload to intercept. Watch the Network tab of your developer tools while you check a CSV file for problems: the only requests are for this site’s own code, and none carries your file.

Your file is processed in this page and never uploaded — the privacy page shows how to confirm that yourself.

Common problems this solves

Excel stops at 1,048,576 rows — here is how to open the rest — Excel silently drops every row past 1,048,576, and saving makes it permanent. Open, check and query the whole file in your browser — nothing uploaded.
My CSV opened as one column — Excel used semicolons — A CSV showing everything in column A was saved with semicolons by a European Excel. Why, how to tell, and how to convert it without retyping a number.
Excel removed the leading zeros — get them back and keep them — Excel turns 00412 into 412 on open; saving makes it permanent. Check whether your file still has its zeros, keep them, or put them back — in your browser.
Compare two versions of an Excel file, cell by cell — Two versions of the same workbook, and you need the differences: rows added, removed and changed, down to the cell. Two steps in your browser, no upload.
Get a CREATE TABLE statement from a CSV file — Turn a CSV into a CREATE TABLE statement and INSERTs for Postgres, MySQL, SQLite or SQL Server, column names from the header. In your browser, no upload.
Which separator and encoding does my CSV use? — Comma, semicolon, tab or pipe; UTF-8, Windows-1252 or UTF-16. How to read what a CSV really uses from its first line, and how to convert it. No upload.
Excel dates showing as numbers like 45292 — what they mean and how to convert them — A date column full of five-digit numbers is Excel counting days since 30 Dec 1899. The arithmetic, the traps, and a one-click conversion to real dates.
The file is too large to open — in Excel, Notepad, or anything else — A CSV Excel will not open, Notepad chokes on and Sheets refuses is usually only long. Read it whole, count it, keep the rows you need — on your machine.
Excel shows #### instead of the value — what it means and what is really in the cell — Number signs across a cell mean the column is too narrow, or the value became a negative date. The value is intact; here is how to see it and keep it.
CSV UTF-8 or plain CSV — which one to save from Excel, and why the accents break — Excel offers CSV and CSV UTF-8. Pick the wrong one and accents and non-Latin names come out as ? or Ã©. Which to pick, and how to repair a file.
Excel says the file format and extension don't match — what the file really is — The warning means the file is not what its name says — usually a web page of a table, or plain CSV, named .xls. How to tell, and how to get the rows out.
pandas says "Error tokenizing data. C error: Expected 5 fields, saw 7" — find the row and fix the file — read_csv stopped because a line has more fields than the heading. Find every such row, see why — an unquoted comma, a stray break — and fix the file.
The QuickBooks report export: title lines above the heading, subtotal rows, and getting a plain table — A QuickBooks report export carries the company name above the heading and subtotal rows in the data. Strip them here and get a table any tool reads.
The Salesforce report CSV: the copyright footer, totals rows, and 15- versus 18-character IDs — A Salesforce report export ends in a copyright footer and may carry a totals row; IDs come in two lengths. Drop the footer and match IDs, in your browser.
The Google Analytics CSV: comment lines above the heading, a second table underneath, and numbers with commas — A Google Analytics download starts with # lines, ends with a second table, and writes numbers with commas and dates as 20240131. Make it one clean table.
The Etsy CSV downloads: orders in one file, items in another, and the statement that explains the fees — Etsy splits a sale across three downloads: orders, order items, and the monthly statement. Which holds what, and how to join them by order id here.
Why a German CSV opens as one column — and what 1.234 means — A German export uses semicolons between fields and a decimal comma. Why 1.234 is one thousand, not one point two, and how to convert the file safely.
A French CSV: semicolons, decimal commas, and a space you cannot see — French exports use semicolons and group thousands with a space that is often a no-break space. What converts automatically here, and what does not.
A Dutch CSV: semicolons, decimal commas, and dates written with dashes — Dutch exports use semicolons and a decimal comma, and write dates 31-12-2026 — dashes that look like an ISO date in the wrong order. How to read one.
A Spanish CSV: semicolons, decimal commas, and identifiers that lose their zeros — Spanish exports use semicolons and a decimal comma. The quieter problem is reference numbers with leading zeros that a spreadsheet throws away on opening.
An Italian CSV: semicolons, decimal commas, and accents that arrive broken — Italian exports use semicolons and a decimal comma, and often arrive as Windows-1252, which is why città shows up as cittÃ . How to read one properly.
A Swedish CSV: the dates are already right, the numbers are not — Swedish exports already write dates the international way, so only the separator and the numbers need work — and a thousands space stops those converting.
A Swiss CSV: semicolons, a decimal point, and apostrophes inside the numbers — Switzerland writes 1'234.56: apostrophe thousands, decimal point, no comma. Why the usual European conversion does nothing here, and what to do instead.
An American CSV abroad: the dates are the thing that breaks — An American CSV opens cleanly almost everywhere, which is the problem: its month-first dates are read as day-first by half the world, silently.
A British CSV: it looks American, and the dates are the other way round — A British CSV uses commas and a decimal point like an American one, but writes dates day first. The two look alike until a date passes the twelfth.
Import customers into Shopify: one row per email, UTF-8, and tags in quotes — Shopify keeps only the last row sharing an email or phone. Choose which one survives, and fix the encoding errors behind Illegal quoting, here first.