Everything runs in your browser. Strict mode (on by default) never sends column samples.
Scan → Review → Apply
See exactly what will change before anything is modified. Undo any step.
Reusable recipes
Download a recipe JSON. Drop it with next month’s file to replay the same steps.
What is spreadsheet cleaning?
Spreadsheet cleaning is turning a messy CSV or Excel export into a consistent table: one date format, blank cells instead of N/A, no accidental duplicate rows, parsed numbers, and split name or address fields. CleanMySheet does that in the browser with named, reversible steps — not by pasting the file into a chatbot.
How to clean a CSV or Excel file
Drop a .csv, .xlsx, or .xls file. Nothing is uploaded in Strict mode.
Read the scan for duplicates, dates, phones, empties, and names.
Apply Recommended or search presets (CRM, finance, survey).
Preview Original, Cleaned, and Diff. Undo any step.
Export CSV (free: 500 rows), a recipe, and a quality report. No. Files stay in your browser. If you join the Pro waitlist we store only the email you give us so we can notify you when sign-in and checkout are live.
Is it safe to upload customer data to an online CSV cleaner?
Only if the tool processes in the browser. CleanMySheet’s Strict mode (default on) does not send column samples or rows to a server.
What is the best free way to clean a CSV file online?
Use a client-side cleaner like CleanMySheet: drop the CSV, apply trim/dates/dedup presets, preview the diff, and export. Strict mode keeps the file on your device. Free export is 500 rows. Can I clean Excel XLSX in a browser?
Yes. CleanMySheet parses XLSX with SheetJS, including multi-sheet workbooks and serial dates, without up the file in Strict mode.
How do I remove duplicate rows in Excel without losing similar contacts?
Run exact dedup for identical rows, then fuzzy matching for near-duplicates. CleanMySheet flags John Smith vs Jon Smith for review instead of auto-deleting.
How do I fix mixed date formats in a spreadsheet?
Parse each cell from the column’s own samples (day-first vs month-first), plus Excel serials, then write one output format. Default is YYYY-MM-DD. Ambiguous values like 03/04/2022 are left alone unless the rest of the column makes the order obvious.
How many rows can I export for free?
You can preview the whole file. Free CSV export is capped at 500 rows. Recipe JSON and the quality report are not row-capped.
Can I reuse the same cleaning steps next month?
Download a .cleanmysheet.json recipe. Drop it with the new CSV to append the same operations. Matching headers also trigger a local recall prompt.
Ready to clean your spreadsheet?
Free export 500 rows. No account needed.
Drop CSV or Excel here
Tap to choose a file. Parsing stays on this device.
Parsing stays on this device. Optional: drop a .cleanmysheet.json recipe with it.
Free export is 500 rows. Pro ($9/mo) launching soon.