Duplicate Line Finder

Find duplicate items in a list, see counts and extract unique entries

What is it and how does it work?

A duplicate finder scans a list of items and identifies which values appear more than once. While a deduplicator removes duplicates and returns unique items, a duplicate finder highlights the repeated entries themselves — useful when you need to investigate or act on the duplicates rather than just discard them. Common scenarios include auditing data quality, finding double-booked entries, and catching repeated submissions in form data.

This tool accepts any text list (one item per line) and returns the duplicates along with how many times each appears. Options include case-insensitive matching (so "ERROR" and "error" count as the same), whitespace trimming before comparison, and sorting the results by frequency (most-duplicated first) or alphabetically. You can also choose to show all duplicate occurrences (every line that is a duplicate) versus just the duplicate values with counts.

Common use cases

• Form submissions: paste a column of email addresses from a registration form to find which emails submitted multiple times, indicating double-registrations or bots.
• Inventory audit: upload a SKU list from two warehouse locations to find product codes that appear in both, flagging potential double-counting in a combined report.
• Log analysis: find repeated error codes in a server log export to identify which errors are recurring versus one-off issues.

Frequently asked questions

What is the difference between a duplicate finder and a deduplicator?

A deduplicator removes duplicates and returns the unique set. A duplicate finder returns the duplicates themselves — the items that appeared more than once. They serve opposite use cases: deduplication cleans data for use; duplicate finding audits the data before deciding what to do.

Does it find near-duplicates or only exact matches?

This tool finds exact duplicates (after optional case-normalisation and whitespace trimming). Near-duplicate or fuzzy matching (e.g., "Jon Smith" vs "John Smith") requires edit-distance algorithms and is a separate, more complex tool.

Can I find duplicates across two separate lists?

Paste both lists one after the other into the input — the tool will find values that appear in both. If you need to see which items are exclusively in list A vs list B, a set difference or diff tool is more appropriate.

Will very large lists cause performance problems?

Browser-based tools handle lists of tens of thousands of lines comfortably. For millions of rows, a command-line tool (sort | uniq -d) or a database query is faster and avoids browser memory limits.

Data

CSV Viewer · Data Faker · List Sorter · Number List Statistics · Array / Set Operations · Tally Counter