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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 to find duplicate values in a spreadsheet
- 1
Upload your spreadsheet
Drag and drop a .csv, .xlsx, or .xls file (up to 5 MB) into the upload box, or click to browse. For Excel workbooks, the first worksheet is analyzed.
- 2
Choose the columns to check
All columns are checked by default. Click a column chip to exclude columns where repeated values are normal, such as city, country, or status.
- 3
Review the highlighted duplicates
Every value that appears more than once in a column is highlighted in amber in the grid, and the summary table counts duplicate values, duplicate cells, and unique values per column.
- 4
Clean up the data
Fix small lists by hand in your editor, or use the FolderManifest desktop app to remove or merge duplicate rows automatically and export a cleaned file — including deduping across several spreadsheets at once.
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.
What people clean with this tool
- Email & subscriber lists — catch duplicate addresses before a campaign goes out twice to the same person.
- CRM & lead exports — dedupe contacts before importing them into a new CRM or outreach tool.
- Order, invoice & transaction IDs — spot double entries that cause double billing or inflated revenue numbers.
- Product SKUs & inventory sheets — make sure every SKU appears exactly once before syncing to a store.
- Survey & form responses — find repeated submissions from the same email or respondent ID.
- Mailing & membership lists — clean up names and addresses merged from several sources.
This tool vs. Excel and Google Sheets built-ins
| Capability | This free tool | Excel | Google Sheets |
|---|---|---|---|
| Highlight duplicates instantly | Yes — automatic on upload | Manual conditional-formatting rule per range | Custom COUNTIF formula per range |
| Per-column duplicate counts | Yes — automatic summary | No — needs helper formulas | No — needs helper formulas |
| Works on CSV files directly | Yes | Opens, but formatting is lost on save | Must be imported first |
| Ignores case and extra spaces | Yes — by default | No — exact match only | No — exact match only |
| Preview duplicates before removing | Yes — highlight-only, nothing changed | No — Remove Duplicates deletes immediately | No — Remove duplicates deletes immediately |
| Nothing to install or sign in to | Yes — runs in your browser | Requires Excel | Requires a Google account |
Prefer to stay inside your spreadsheet app? See our step-by-step guides to finding duplicates in Excel and finding duplicates in Google Sheets.
Frequently asked questions
How do I find duplicate values in a spreadsheet?
Upload your CSV or Excel file to this free tool. It highlights every value that appears more than once in each column and shows a per-column count of duplicates. Everything runs in your browser — the file is never uploaded.
How do I find duplicates in Excel without deleting them?
Upload the Excel file here. Every duplicate value is highlighted in amber but nothing is changed or removed, so you can review each repeated value before deciding what to delete. Excel’s built-in Remove Duplicates deletes rows immediately without showing you which values matched.
Does my spreadsheet get uploaded to a server?
No. The tool parses and analyzes your file entirely in your browser using JavaScript. Your data never leaves your computer, so it is safe for confidential lists like customers, leads, or finance data.
What file formats are supported?
CSV (.csv) and Excel (.xlsx, .xls). For Excel files, the first worksheet is analyzed. Files up to 5 MB and the first 1,000 rows are processed in the browser; the FolderManifest desktop app handles unlimited rows and files.
Can I check a Google Sheets spreadsheet for duplicates?
Yes. In Google Sheets, go to File → Download → Comma-separated values (.csv), then upload the downloaded file here. The tool highlights the duplicate values and counts them per column, with no COUNTIF formulas or conditional formatting rules needed.
How do I remove the duplicates I find?
This free tool highlights duplicates so you can review them. To export a cleaned, deduplicated file or remove and merge duplicate rows automatically, use the FolderManifest desktop app, which also dedupes across many spreadsheets at once.
Can I choose which columns to check for duplicates?
Yes. Use the column picker to include or exclude any column. By default every column is checked. Duplicates are detected per column — a value is flagged when it appears more than once in the same column.
Is the duplicate match case-sensitive?
No. Values are compared case-insensitively and with surrounding whitespace ignored, so "John Smith" and "john smith " are treated as the same value. Empty cells are never flagged as duplicates.
What is the difference between this tool and Excel’s Remove Duplicates?
Excel’s Remove Duplicates deletes matching rows in one step without previewing which values were duplicated. This tool is the audit step: it shows every duplicate value, highlighted in place with per-column counts, so you can verify before removing anything. When you are ready to clean the file, the FolderManifest desktop app removes or merges the duplicate rows and exports the result.
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