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Find Duplicate Lines Online — Free Duplicate Line Detector

Instantly detect duplicate lines in any text with color-coded visual highlighting. Paste your content, and each group of duplicates is assigned a distinct color so you can spot repeats at a glance. Supports case-insensitive matching — "Grafik Onboard", "Grafik onboard", and "Grafik onBoard" are all treated as one duplicate group. Runs entirely in your browser — no data is sent to any server.

Features

  • Color-coded groups

    Each duplicate group gets a unique color so you can visually distinguish multiple groups in a single pass.

  • Case-insensitive matching

    Toggle case sensitivity to match lines regardless of capitalization, perfect for names, tags, or keywords.

  • Trim whitespace

    Optionally strip leading and trailing spaces before comparing, so " hello " and "hello" are treated as identical.

  • Line number references

    Each duplicate group shows the exact line numbers where it appears, making it easy to locate and fix them.

  • Copy actions

    Export the deduplicated text (first occurrence kept) or a list of just the duplicate values with one click.

  • Runs locally

    All processing happens in your browser — your text never leaves your device.

How to find duplicate lines online

  1. Paste your textPaste any multi-line content into the input box — a list of names, keywords, log entries, or any text.
  2. Set optionsToggle "Case insensitive" to match lines regardless of capitalization. Enable "Trim whitespace" to ignore leading/trailing spaces.
  3. Review highlighted linesThe Highlighted Lines panel renders every line with color-coded backgrounds. Each duplicate group shares a color, making repeats immediately visible.
  4. Check duplicate groupsThe Duplicate Groups panel lists each repeated value, its occurrence count, and the exact line numbers where it appears.
  5. Export resultsClick "Copy Unique" to copy the deduplicated text, or "Copy Duplicates" to copy only the repeated values.

Examples

Case-insensitive name deduplication

Input
Grafik Onboard
Grafik onboard
Grafik onBoard
Another Item
Another item
Output
2 duplicate groups found:
× 3 — "Grafik Onboard" (lines 1, 2, 3)
× 2 — "Another Item" (lines 4, 5)

Log entry deduplication

Input
ERROR: connection timeout
INFO: server started
ERROR: connection timeout
ERROR: connection timeout
Output
1 duplicate group:
× 3 — "ERROR: connection timeout" (lines 1, 3, 4)

Frequently Asked Questions

What does case-insensitive matching mean?
When case-insensitive mode is on, the tool normalizes all lines to lowercase before comparing them. This means "Grafik Onboard", "grafik onboard", and "GRAFIK ONBOARD" all count as the same line.
What does "Trim whitespace" do?
Trimming removes leading and trailing spaces from each line before comparison. So " hello " and "hello" are treated as identical. This is useful when copying data from spreadsheets or tables that may add extra spaces.
Does the tool send my text to a server?
No. All processing runs entirely in your browser using JavaScript. Your text never leaves your device.
What does "Copy Unique" produce?
"Copy Unique" outputs the full text with duplicates removed — keeping only the first occurrence of each line, preserving the original order.
What does "Copy Duplicates" produce?
"Copy Duplicates" copies only the lines that appeared more than once, with each value included once regardless of how many times it repeated. Useful for building a list of items to fix.
Is there a line limit?
There is no hard limit. The tool handles thousands of lines comfortably. Very large inputs (100k+ lines) may slow down the browser due to DOM rendering.