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.

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 with common tokens and Excel serial numbers, then write one output format (YYYY-MM-DD, DD/MM/YYYY, or MM/DD/YYYY). That is the Standardize dates preset.

Can I clean Excel XLSX in a browser?

Yes. CleanMySheet parses XLSX with SheetJS, including multi-sheet workbooks and serial dates, without uploading the file in Strict mode.

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.

How do I split Full Name into first and last?

Detect Last, First versus First Last on a Name column and insert First Name and Last Name. Do not split city or product columns.

How do I standardize phone numbers in a CSV?

Keep digits, preserve a leading +, and format 10-digit US numbers as (555) 123-4567 or 555-123-4567.

What is spreadsheet data cleaning?

It is turning inconsistent tabular files into a predictable table: one date format, one empty token, no accidental duplicate rows, parsed numbers, and split fields—with an audit of what changed.

CCleanMySheet

CSV & Excel cleaner

Clean spreadsheets in the browser. Nothing is uploaded.

Remove duplicates, standardize dates, split names, and format phones in CSV or XLSX. We scan first and suggest fixes — nothing changes until you click Apply. Strict mode is on by default.

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.

Preview the full file · free export 500 rows · CSV & XLSX

Private by default

Parsing and cleaning run on your machine. Strict mode never sends column samples anywhere.

Shows its work

Scan first, then apply. Toggle any step, undo the last change, hover a cell to see why it moved.

Replay next month

Download a recipe JSON with the CSV. Same columns later? Apply the same clean in one click.

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.

Popular cleanups

Clean a CSV online without uploading it
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Remove duplicate rows from a spreadsheet
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Find near-duplicate rows (fuzzy matching)
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Standardize mixed date formats in a spreadsheet
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Split names in a CSV (Last, First and First Last)
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Format phone numbers in CSV or Excel
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All guides · FAQ

Questions people ask

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.
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 with common tokens and Excel serial numbers, then write one output format (YYYY-MM-DD, DD/MM/YYYY, or MM/DD/YYYY). That is the Standardize dates preset.
Can I clean Excel XLSX in a browser?: Yes. CleanMySheet parses XLSX with SheetJS, including multi-sheet workbooks and serial dates, without uploading the file in Strict mode.
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.
How do I split Full Name into first and last?: Detect Last, First versus First Last on a Name column and insert First Name and Last Name. Do not split city or product columns.
How do I standardize phone numbers in a CSV?: Keep digits, preserve a leading +, and format 10-digit US numbers as (555) 123-4567 or 555-123-4567.
What is spreadsheet data cleaning?: It is turning inconsistent tabular files into a predictable table: one date format, one empty token, no accidental duplicate rows, parsed numbers, and split fields—with an audit of what changed.

Free export is 500 rows. Pro removes the cap.