Compare Files Online
Upload 2 files to instantly check if they are identical using SHA-256 checksums.
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Find Duplicate Values in CSV & Excel
Upload a CSV or Excel file (up to 5 MB, 1,000 rows) to instantly highlight duplicate values and see a per-column duplicate count. 100% private — your file never leaves your browser.
Upload a spreadsheet
Drag & drop a CSV or Excel file, or click to browse (one file, max 5 MB).
Drag & drop your CSV or Excel file
or click to browse · .csv, .xlsx, .xls
What this tool can and can't do
✅ What it does
- • Highlights duplicate values per column in CSV and Excel files
- • Shows a per-column duplicate count summary
- • Runs 100% in your browser — your data never leaves your computer
- • Lets you pick which columns define a duplicate
❌ What it doesn't do
- • Doesn't export a cleaned/deduplicated file (desktop only)
- • Doesn't remove or merge duplicate rows automatically (desktop only)
- • Doesn't dedupe across multiple spreadsheets at once (desktop only)
- • Processes the first 1,000 rows of files up to 5 MB
How duplicate detection works
The tool reads your spreadsheet in the browser, then checks each selected column independently. A value is a duplicate when it appears more than once in the same column. Matching ignores letter case and surrounding spaces, and empty cells are never flagged.
Every duplicate cell is highlighted in amber, and the summary table counts how many duplicate values and duplicate cells each column contains — so you can see at a glance which column (emails, order IDs, SKUs, phone numbers) has the data-quality problem.
Private by design
Unlike many online duplicate checkers, this tool never uploads your file. Parsing and analysis happen entirely in your browser with JavaScript, so confidential lists — customers, leads, payroll, patient records — stay on your machine. When you need to clean files at scale or keep an audit trail, the FolderManifest desktop app does it offline on your own computer.
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