Find Duplicate Lines
Find repeated lines and show how many times each exact line occurs. This is a review tool: it reports duplicates without changing your source text.
What this tool actually changes
The tool counts each exact input line with a JavaScript Map, then reports only entries whose count is greater than one. Results retain the order in which each distinct line was first encountered.
Edge cases to know
Comparison is exact and case-sensitive. Whitespace is significant, so alpha and alpha with a leading space are different lines. Blank lines are counted too if they occur more than once.
Example
Input: alpha beta alpha gamma beta Output: alpha (2) beta (2)
Good use cases
Checking exported data, repeated identifiers, copied configuration, lists, and logs before deciding whether duplicates should be removed.
Workflow tip
Choose the operation that matches your intent. If whitespace is causing unexpected duplicates, normalize it before deduplicating rather than assuming the duplicate operation should ignore formatting.
Frequently asked questions
Does it remove duplicates?
No. It reports repeated lines and their counts without modifying the input.
Are counts case-sensitive?
Yes. Lines are compared exactly, including capitalization and whitespace.
Can it find repeated blank lines?
Yes. Blank lines are ordinary input lines and are counted if they repeat.