How it works
Build exact composite keys from the selected cells. Return every row whose key occurs more than once, with the occurrence count.
Input definitions
- CSV with headers
- Plain text; maximum 200,000 characters.
- One exact key column name per line
- Plain text; maximum 200,000 characters.
A worked example
- CSV with headers
- id,name 1,Ada 2,Lin 1,Sam
- One exact key column name per line
- id
Assumptions & limits
Browser-local processing. CSV uses one unique header row, at most 1,000 total input rows and 50 columns. Downloads escape spreadsheet formula prefixes.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
How is a duplicate key different from a duplicate row?
Rows can share an ID while their other columns differ. This tool flags the selected key combination instead of requiring every cell to match.
How does Find duplicate CSV keys work?
Build exact composite keys from the selected cells. Return every row whose key occurs more than once, with the occurrence count.
What are the limits of Find duplicate CSV keys?
Browser-local processing. CSV uses one unique header row, at most 1,000 total input rows and 50 columns. Downloads escape spreadsheet formula prefixes.
How do I keep the full worksheet?
Run the tool and choose Download file. The on-page table is a preview and may show only the first 20 rows; the downloaded file contains the full result. CSV downloads escape spreadsheet formula prefixes. Inputs and files are processed on your device.